UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


GIFT  OF 

CARNEGIE   INSTITUTION 
OF   WASHINGTON 


GROWTH  IN  TREES 


BY 

D.  T.  MACDOUGAL 


PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 
WASHINGTON,  1921 


8T43 


GROWTH  IN  TREES 


BY 

D.  T.  MAcDOUGAL 


PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 
WASHINGTON,  1921 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
PUBLICATION  No.  307 


PRESS   OF   GIBSON   BROS.,    INC. 
WASHINGTON,  D.  C. 


GROWTH  IN  TREES. 


BY  D.  T.  MACDOUGAL. 


A  tree  may  be  considered  as  a  tall  cone  of  wood  terminating  in  leafy 
expanses.  The  base  of  the  cone  is  subdivided  into  myriads  of  rootlets, 
through  the  surfaces  of  which  the  soil-solutions  enter,  and  the  water, 
pas?ing  upward,  is  transpired  from  the  leaves.  The  trunk  of  a  tree 
is  largely  composed  of  dead  cells,  but  inclosing  it  is  a  thin  sheet  of 
spindle-form  cambium  cells1  in  2  to  10  or  more  layers,  which  in  the 
growing  season  enlarge  in  thickness  and  divide  lengthwise,  those  on  the 
outside  becoming  transformed  into  cork  and  phloem  and  those  on  the 
inner  into  wood  cells  and  vessels.  Extending  from  the  center  of  the 
trunk  are  thin  sheets  or  rays  of  the  medulla  or  pith  of  the  young  stem. 
The  most  recently  formed  cells  of  these  elements  are  still  living  and  in 
some  trees  the  medullary  cells  remain  alive  for  several  years,  so  that 
the  woody  cylinder  of  the  tree  may  comprise  wood-cells  or  tracheids, 
vessels,  and  thin-wall  ray  cells,  some  of  which  are  alive.  External  to 
the  cambium  are  sieve  cells,  bast  fibers,  etc.,  and  cork  cells,  inclosed  in  a 
bark  which  varies  widely  as  to  structure  in  different  species. 

The  greatest  amount  of  increase  or  change  in  volume  is  that  which 
results  from  the  multiplication  by  fission  of  the  cambium  cells,  and 
their  enlargement  accompanied  by  the  differentiations  mentioned,  all 
based  upon  hydration  of  cell-colloids. 

When  changes  in  the  entire  diameter  are  measured  the  variations 
may  be  due  to  the  action  of  any  one  of  these  tracts  of  tissue.  The 
colloids  of  the  cell,  including  those  of  non-living  walls  or  wood,  are 
practically  never  in  a  stable  condition,  but  follow  an  ever-varying 
environment  in  resultant  adjustments,  especially  with  respect  to  the 
water  which  they  contain.  All  plants  except  submerged  forms  are 
always  losing  water  at  a  varying  rate  from  part  of  their  surfaces,  while 
water  may  be  entering  absorbing  surfaces  at  a  varying  rate,  and  as  a 
consequence  of  the  inequality  the  volume  may  increase  or  decrease 
according  to  the  balance  between  gain  and  loss. 

Growth  in  organisms  is  essentially  a  hydration  of  colloids  of  the 
protoplasm  accompanied  by  metabolic  changes  which  result  in  the 
conversion  of  materials  in  the  cell-sap  to  the  emulsoid  condition  charac- 
teristic of  living  matter.  Both  processes,  one  of  adsorption  and  the 
other  a  result  of  shifting  equilibria  in  chemical  systems,  cause  an 

1  Bailey,  I.  W.  Phenomena  of  cell-division  in  the  cambium  of  arborescent  gymnosperms  and 
their  cytological  significance.  Proc.  Nat.  Acad.  Sci.,  5:  283-285.  1919. 


209253 


4  GROWTH   IN   TREES. 

increase  of  the  volume  of  the  protoplasm  and  an'enlargement  of  the 
cell-mass  of  which  it  forms  a  part. 

Any  instrumentation  of  sufficient  accuracy  and  delicacy  to  measure 
the  increases  or  variations  due  to  growth  in  the  cambium  layer  will  at 
the  same  time  include  the  variations  in  volume  of  the  woody  cylinder, 
which  is  also  the  conduit  through  which  liquid  passes  from  the  roots 
to  the  crown.  Similar  conditions  prevail  in  nearly  all  higher  plants, 
and  growth  measurements  of  all  stems,  leaves,  and  roots  include 
changes  in  woody  or  non-living  cells. 

Such  trees  as  the  birch,  with  200,000  leaves,  are  reputed  to  transpire 
as  much  as  400  liters  in  a  single  day.  No  estimates  of  the  pines  are 
available,  but  the  low  moisture  content  of  the  soil  around  the  roots  of 
the  Monterey  pine  would  not  furnish  a  supply  for  such  use  of  water. 
The  trunk  of  a  tree  may,  in  fact,  be  compared  to  the  supply  hose  of  a 
fire-engine  coupled  to  a  hydrant.  When  the  pressure  from  the  mains 
is  enough  to  supply  water  faster  than  it  can  be  pumped  out,  the  hose  is 
distended.  When  the  engine  tends  to  take  water  faster  than  it  would 
be  delivered  by  the  system,  the  hose  would  tend  to  collapse.  Some- 
thing of  this  sort  takes  place  in  many  trees  which  have  been  kept  under 
observation.  The  conduit  in  this  case,  however,  is  not  a  simple  pipe 
or  a  set  of  pipes,  but  is  made  up  of  vessels,  through  which  water  may 
pass  under  capillary  conditions,  and  inclosed  box-like  tracheids  which 
may  be  only  partially  filled  with  water.  When  water  is  withdrawn 
from  such  a  system  faster  than  it  is  taken  in,  the  resulting  changes  in 
form  and  size  are  complex  hi  character. 

These  facts  were  well  considered  in  my  experiments  previously 
carried  out  when  the  measurement  of  growth  in  trees  was  taken  up 
in  1918,  and  a  new  technique  with  specially  designed  instruments 
was  found  necessary  for  the  analytical  study  of  the  changes  in  volume 
of  these  massive  organs.  The  records  are  now  continuous  for  a  large 
number  of  trees  for  many  months,  one  tree  having  been  under  con- 
tinuous measurement  since  September  1919.  The  chief  features 
considered  in  the  present  paper  are  as  follows: 

1.  The  dendrograph,  an  instrument  for  making  continuous  records 
of  the  variation  of  tree  trunks,  has  been  developed  to  an  approximately 
final  form.1  The  essential  feature  of  this  instrument  consists  of  a 
floating  frame  of  metal  of  low  temperature  coefficient,  such  as  invar 
or  bario,  which  may  be  placed  around  a  tree  trunk,  and  the  variation 

^acDougal,  D.  T.     The  dendrograph:  a  new  instrument  for  recording  growth  and  other  varia- 
tions in  the  dimensions  of  trees.     Carnegie  Inst.  Wash.  Year  Book  for  1918,  pp.  59-60. 

.     The  dendrograph.     Carnegie  Inst.  Wash.  Year  Book  for  1919,  pp.  72-78. 

.     The  course  of  growth  in  trees  as  measured   by   the  dendrograph.     Carnegie   Inst. 

Wash.  Year  Book  for  1920,  pp.  51-52. 

.     Measurement  of  a  season's  growth  of  trees  by   the   newly   designed   dendrometer. 

Carnegie  Inst.  Wash.  Year  Book  for  1920,  p.  52. 
A  brief  discussion  of  the  contents  of  the  present  paper  was  given  before  the  American 

Philosophical  Society  at  Philadelphia,  April  22,  1921,  which  is  in  press  in  the  Proceedings  of 

the  Society. 


GROWTH    IN   TREES.  5 

in  distance  between  a  contact  rod  on  one  side  of  the  trunk  and  of  one 
end  of  a  rod  or  lever  on  the  other  side  is  traced  by  a  pen  on  the  free 
end  of  a  lever  on  a  sheet  of  paper  carried  by  a  recording  cylinder. 
Such  measurements  are  in  terms  of  the  diameter. 

2.  A  dendrometer,  of  simple  design  and  non-expensive  construction, 
has  been  perfected,  which  may  be  placed  around  the  trunk  of  a  tree 
and  the  size  of  the  trunk  read  on  a  dial  from  time  to  time.     The 
essential  parts  of  this  instrument  are  an  encircling  wire  engaged  with 
a  number  of  bearing  levers.     One  end  of  the  wire  is  anchored  and  the 
other  is  attached  to  the  short  end  of  a  lever,  the  free  end  of  which  moves 
over  a  scale  giving  readings  of  the  size  of  the  trunk  in  terms  of  several 
radii,  or  of  the  circumference. 

3.  Dendrographic  records  of  trees  have  been  made  as  follows: 

Citrus  aurantica:  Citrus  Experiment  Station,  Riverside,  California;  by  H.  S.  Reed. 

Fagus  grandifolia:  Baltimore,  Maryland;  by  B.  E.  Livingston. 

Fraxinus  arizonica:  Tucson,  Arizona;  by  H.  W.  Fenner. 

Juglans  major:  Carmel,  California;  by  D.  T.  MacDougal. 

Parkinsonia  microphylla:  Tucson,  Arizona;  by  B.  R.  Bovee. 

Picea  pungens:  Cottonwood  Nursery,  Wasatch  Mountains,  Utah;  by  C.  F.  Korstian. 

Pinus  chihuahuana:  6,000  feet  altitude,  Santa  Catalina  Mountains,  Tucson,  Arizona;  by 

D.  T.  MacDougal  and  B.  R.  Bovee. 
Pinus  ponderosa:  Alpine  Laboratory,  Pikes  Peak,  Colorado;  by  F.  E.  Clements  and  Gorm 

Loftfield. 

Pinus  radiata:  Seven  trees,  Carmel,  California;  by  D.  T.  MacDougal. 
Pinus  scopulorum  Lemmon:  Fort  Valley  Experiment  Station,  Flagstaff,  Arizona;  by  G. 

A.  Pearson. 

Platanus  occidentalis:  Missouri  Botanical  Garden;  by  B.  M.  Duggar  and  F.  S.  Walpert. 
Populus  deltoides:  Missouri  Botanical  Garden,  by  B.  M.  Duggar  and  F.  S.  Walpert. 
Populus  macdougalii:  Continental,  Arizona;  by  W.  B.  McCallum. 
Pseudotsuga  mucronata  Sudworth:   Alpine  Laboratory,  Pikes  Peak,  Colorado;  by  F.  E. 

Clements  and  G.  Loftfield. 
Quercus  agrifolia:  two  trees,  Carmel,  California;  by  D.  T.  MacDougal. 

4.  The  trees  noted  above  represented  deciduous  and  evergreen 
coniferous  types  native  to  the  Atlantic  seaboard,  the  Mississippi  valley, 
various  elevations  hi  the  Rocky  Mountains,  the  plateau,  mountain 
slopes,  and  desert  valleys  of  Arizona,  the  plains  of  southern  California, 
and  the  coastal  region  at  Carmel,  with  a  wide  variety  of  climatic  con- 
ditions and  seasons. 

5.  The  period  in  which  enlargement  of  trunks  takes  place  is  com- 
paratively brief,  even  in  places  in  which  the  season  is  of  indeterminate 
duration. 

6.  Growth  is  an  activity  of  an  embryogenic  tract  of  tissue,  which 
depends  upon  environmental  conditions,  and  no  part  of  the  observa- 
tions suggested  a  seasonal  rhythmic  action.     The  Chihuahua  pine, 
which  exhibits  growth  of  the  trunk  with  that  of  the  branches  on  the 
dry  mountain  slopes  in  the  advance  of  the  temperatures  in  May  and 
June,  is  brought  to  rest  coincident  with  the  desiccation  of  the  soil  in 
the  dry  fore-summer.     Reawakening  ensues  consequent  upon  the  sum- 
mer rains,  and  enlargement  continues  until  checked  by  the  decreasing 
temperatures  and  increased  soil  desiccation  in  the  autumn.     The 


6  GROWTH   IN   TREES. 

Monterey  pine  (Pinus  radiatd)  shows  beginning  growth  of  the  trunks 
with  the  advance  of  temperatures,  January  to  April,  and  comes  to 
rest  in  July  with  the  desiccation  of  the  soil.  Quercus  agrifolia  in  the 
same  region  begins  earlier  and  ceases  to  grow  in  June  or  July.  Both 
may  be  awakened  in  July  or  August  by  deep  irrigation  of  the  soil. 

7.  The  trunks  of  all  the  trees  measured  show  a  daily  variation  in 
size,  by  which  the  maximum  is  reached  shortly  after  sunrise  and  the 
minimum  at  a  time  after  noon,  dependent  upon  external  agencies. 
These  variations  appear  to  depend  upon  the  water-balance  in  the 
woody  cylinder,  are  greatest  in  the  seasons  in  which  water-loss  from 
the  crown  is  greatest,  are  least  in  the  cooler  or  damper  seasons,  and 
are  to  be  detected  in  the  records  even  in  the  period  of  most  rapid 
enlargement  of  the  trunk. 

8.  Measurement  of  variations  in  the  woody  cylinder  were  taken  by 
arranging  the  contact  rods  of  the  dendrograph  to  bear  on  the  wood 
formed  by  the  tree  two  years  previously.     Thus,  in  1920  holes  were 
bored  through  the  wood  of  that  year  and  of  1919  and  contacts  made 
at  the  bottom  of  the  cavities. 

9.  In  general  the  awakening  and  growth  of  the  terminal  buds  with 
resultant  elongation  of  leaders  and  branches  begins  in  many  trees  some 
time  before  enlargement  of  the  trunk  takes  place.     The  period  sepa- 
rating the  two  may  be  no  more  than  a  week  in  Quercus  agrifolia 
and  has  been  seen  to  be  as  much  as  10  or  12  weeks  in  Pinus  radiata. 
Observations  on  the  Parry  spruce  and  Douglas  fir  show  that  the  trunks 
of  these  trees  are  enlarging  at  a  time  when  the  buds  are  in  a  very 
early  stage  of  enlargement. 

10.  In  the  single  case  in  which  dendrographs  were  attached  to  a 
pine  tree  1  meter  and  8  meters  above  the  ground,  growth  began  coin- 
cidentally  at  the  two  places  in  1920.     In  the  following  year,  however, 
the  dendrograph  at  the  higher  point  on  the  trunk  recorded  enlargement 
a  few  days  before  any  action  near  the  ground  was  made  visible.     In 
February  1921  an  auxograph  was  brought  into  bearing  on  the  inter- 
node  of  a  pine  tree  5  or  6  years  old  which  had  been  formed  in  1919. 
The  buds  had  made  a  growth  of  4  or  5  cm.,  but  no  action  had  yet 
begun  in  the  internode.     A  second  instrument  was  brought   into 
bearing  on  the  middle  of  the  internode  formed  in  1920  on  another  young 
tree.     Steady  enlargement  was  in  progress. 

11.  The  embryonic  layer  of  a  tree  is  in  the  form  of  an  inclosing  sheath 
terminating  in  the  cones  of  the  growing  points.     Activation  of  this 
tract  is  generally  initiated  in  the  growing  points.     Swelling  in   the 
cambium  layer  may  be  practically  coincident  with  this  awakening  in 
some  trees.     Cases  are  recorded  in  the  present  paper  in  which  weeks 
elapsed  between  the  awakening  of  the  buds  and  the  enlargement 
of  the  base  of  the  trunk.     Activation  of  the  growing  cells  may  be  taken 
to  depend  upon  the  localized  food-supply,  temperature,  moisture,  or 
other  factors. 


GROWTH   IN   TREES.  7 

12.  Estimates  of  the  range  of  daily  equalizing  variations  in  a  Mon- 
terey pine  taken  from  bearings  on  a  thin  layer  of  cork  external  to  the 
bast  of  a  trunk  which  had  ceased  to  grow  for  the  season  show  that  the 
diameter  might  vary  1  part  in  1,750.     That  a  large  share  of  this  varia- 
tion is  due  to  changes  in  the  hydration  of  the  living  cells  is  proved  by 
the  fact  that  when  bearings  are  taken  on  the  woody  cylinder  of  the 
trunk  internal  to  the  growing  layer  the  variation  drops  to  1  part  in 
8,750  of  the  diameter.     The  actual  change  in  volume,  in  the  first 
instance  calculated  on  the  basis  of  a  conical  trunk  18  meters  high  and 
35  cm.  in  diameter  at  the  base,  would  amount  to  about  400  cu.  cm., 
of  which  not  more  than  one-fifth,  or  80  cu.  cm.,  is  attributable  to  varia- 
tions in  the  wood.     It  is  to  be  noted,  however,  that  the  change  in  the 
volume  of  the  wood  may  by  no  means  be  taken  to  represent  the  water 
deficit  in  the  wood.    The  woody  mass  is  made  up  of  box-like  cells, 
which  may  include  a  bubble  of  gas,  the  water  forming  no  more  than  a 
thin  film  on  the  wall  of  the  cell  and  inclosing  the  gas  bubble  in  the 
condition  of  extreme  water  deficit.     The  withdrawal  of  water  through 
the  walls  of  the  cells,  which  are  semi-rigid,  increases  the  surface  ten- 
sion of  the  gas  bubble,  which  results  in  a  slight  lessening  of  volume  of 
the  whole  mass,  but  in  an  amount  that  would  constitute  no  more  than 
a  small  fraction  of  the  total  of  the  water  loss. 

13.  Of  15  trees  which  were  under  dendrographic  measurement  in 
1920,  one  each  of  Pinus  scopulorum,  Citrus  aurantica,  and  Parkinsonia 
microphylla  made  no  enlargement  during  the  year.     Such  occurrences 
are  to  be  taken  into  account  in  estimations  of  the  ages  of  trees  from 
the  annual  layers. 

14.  The  greatest  daily  equalizing  variations  were  shown  by  Frax- 
inus,  Pinus,  Picea,  Pseudotsuga,  and  Juglans,  and  lesser  variations 
were  displayed  by  Populus,  Platanus,  Fagus,  Quercus,  and  Citrus. 
No  available  facts  furnish  the  basis  of  an  adequate  explanation  of  such 
differences. 

15.  The  final  effect  of  rainfall  shown  within  a  few  hours  is  to  accel- 
erate growth,  but  it  has  been  repeatedly  observed  that  actual  shrink- 
age may  take  place  while  the  rain  is  falling.     This  action  can  not  be 
traced  to  any  instrumental  error. 

16.  Irrigation  of  the  soil  which  had  a  moisture  content  of  less  than 
6  per  cent  around  the  roots  of  a  Monterey  pine  was  followed  within 
24  hours  by  progressive  enlargement  constituting  growth  at  the  base 
of  the  tree,  and  at  a  point  8  meters  higher.     The  distance  from  the 
absorbing  surfaces  of  the  roots  through  which  the  added  water  supply 
must  enter  could  not  be  less  than  3  meters  from  the  lower  instrument, 
and  the  influence  of  the  added  supply  was  within  the  day  felt  at  the 
upper  instrument,  11  meters  from  the  absorbing  surfaces.     It  does  not 
seem  possible  that  water  could  have  been  conducted  through  the 
tracheids  this  distance  within  the  given  length  of  time. 


8  GROWTH   IN   TREES. 

17.  An  irrigation  test  similar  to  the  above  was  made  with  a  small 
California  live  oak  (Quercus  agrifolia).     The  results  were  even  more 
startling  than  those  described  for  the  pine.     Within  two  hours  the 
dendrograph,  which  had  its  contacts  with  the  tree  at  least  3  meters 
from  the  absorbing  surfaces,  showed  some  enlargement,  an  action 
which  may  be  directly  connected  with  the  fact  that  the  vessels  in  this 
oak  are  numerous  and  large. 

18.  The  irrigation  experiments  might  be  held  to  simulate  the  effects 
of  stream  overflow  which,  if  due  to  melting  snows,  would  not  be  accom- 
panied by  any  marked  higher  humidity.    It  is  seen  to  result  in  the 
formation  of  a  tapering  shell  of  wood  which  was  as  thick  as  the  seasonal 
formation  at  the  base  of  the  trunk,  but  which  had  but  half  this  thick- 
ness 8  meters  higher  up  on  the  trunk.     The  layer  of  normal  formation 
was  of  practically  identical  thickness  at  the  two  places. 

HISTORICAL. 

The  rate  and  course  of  growth  in  length  of  seedlings  and  plantlets 
of  various  trees  have  been  the  basis  of  many  measurements,  and  the 
forester  developed  approximate  methods  for  estimating  the  yearly  or 
seasonal  increase  in  the  height  or  diameter  of  trunks.  An  interesting 
series  of  monthly  measurements  of  a  number  of  trees  was  made  at 
San  Jorge,  Uruguay,  in  1885-1890.  Evergreen  trees,  including 
conifers,  eucalyptus,  and  acacia,  showed  greatest  increases  in  October, 
a  spring  month,  and  least  in  July  (midwinter),  while  deciduous  trees 
increase  most  in  midsummer  (December)  and  actually  decrease  in 
girth  in  autumn  (May).1  Recently,  also,  some  calibrations  of  the 
variations  in  volume  of  trunks  correlated  with  temperatures  have 
been  made  in  New  York.2  The  available  data,  however,  did  not  re- 
cord the  daily  and  seasonal  changes  or  include  information  by  the  aid 
of  which  the  activities  of  growing  tips  and  branches  might  be  correlated 
with  changes  in  volume  of  trunks  and  stems. 

The  most  notable  attempt  to  follow  accurately  the  variations  in  tree 
trunks  previous  to  the  instrumentation  described  in  the  present  paper 
was  that  of  Mallock  in  1917.  He  used  an  apparatus  consisting  essen- 
tially of  two  plates  of  glass  superposed,  or  an  arrangement  of  prisms 
in  connection  with  a  tape  of  invar  passed  around  the  tree.  Vaiiations 
in  girth  caused  displacement  of  interference  bands  of  light.  Obser- 
vations on  such  displacements,  at  frequent  intervals,  showed  that 
growth  was  greatest  hi  the  early  part  of  the  day,  that  actual  contraction 
occurred  in  the  afternoon,  and  that  increases  were  closely  related  to 
temperature  and  rainfall.3 

1  Hall,  C.  E.     Notes  on  tree  measurements  made  monthly  at  San  Jorge,  Uruguay,  from  Jan. 
12,  1885,  to  Jan.  12,  1890.     Trans.  Bot.  Soc.  Edinburg,  18:456.     1891. 

2  Trowbridge  and  Weil.    The  coefficient  of  expansion  of  living  tree  trunks.    Science,  48 : 348-350. 
1918. 

*  Mallock.  A.  Growth  of  trees,  with  a  note  on  interference  bands  formed  by  rays  at  email 
angles.  Proc.  Roy.  Soc.,  90,  B,  186-191.  1919.  Submitted  Dec.  1,  1917. 


GROWTH    IN   TREES.  9 

This  ingenious  method  would  enable  the  observer  to  detect  changes 
of  0.00005  inch  in  circumference,  but  as  no  recording  devices  are 
provided  the  constant  attendance  of  the  observer  was  necessary. 
Meanwhile  my  own  results  show  that  an  actual  amplification  of  8  to 
15  times  the  changes  in  diameter  of  the  trunk  is  adequate  for  direct 
observation  and  analysis. 

Friedrich  had  previously  used  a  device  for  recording  increments  to 
the  thickness  of  trees  as  early  as  1905. 1  The  tree  was  encircled 
with  a  steel  band  on  roller  bearings,  and  the  ends  were  attached  to 
both  registering  and  recording  arms.  No  cognizance  was  taken  of 
errors  due  to  changes  in  temperature,  and  no  results  obtained  with 
this  apparatus  have  been  seen. 

Some  success  having  been  attained  in  the  measurement  of  the  varia- 
tions in  stems  such  as  those  of  the  sunflower  (Hehanthus)  and  in  the 
variations  in  volume  of  succulent  stems  such  as  those  of  Opuntia, 
by  the  use  of  mechanical  levers,  it  was  found  desirable  to  extend  the 
observations  to  trees.  It  was  thought  that  accurate  measurements  of 
the  changes  in  volume  of  these  massive  structures  might  not  only 
give  information  of  value  on  the  subject  of  hydration  and  growth,  but 
that  some  light  might  be  thrown  on  the  problem  of  ascent  of  sap. 

The  attempt  to  measure  the  variations  in  large  trunks,  begun  in 
1918,  raised  many  difficult  mechanical  problems.  First  it  was  obvious 
that  it  would  be  practically  impossible  to  hold  the  stem  of  any  but 
small  trees  rigidly  in  any  position.  This  made  it  necessary  to  devise 
means  whereby  the  tree  would  support  the  instruments  and  carry 
them  with  it  as  it  swayed  and  leaned.  It  soon  became  evident  that 
such  an  appliance  should  consist  of  two  parts;  a  base  which  would 
remain  firmly  in  whatever  position  near  the  horizontal  it  might  be 
placed  about  the  trunk,  and  which  would  carry  the  more  delicately 
arranged  members  of  the  second  part  which  would  register  variations  in 
diameter  at  some  little  distance  from  this  base. 

Two  forms  of  base  or  support  were  devised  and  tested.  One  form 
consisted  of  a  rectangular  frame  built  up  of  bands  of  wrought-iron 
2  by  ^  inches  and  of  oak  wood  2  by  2>£  inches,  which  could  be 
clamped  about  the  tree  tightly  by  means  of  an  iron  rod,  including  a 
heavy  turnbuckle.  A  heavy  block  of  seasoned  oiled  wood  at  one  end 
formed  a  base  for  the  levers  and  recorders  and  a  wooden  screw  30  cm. 
long,  working  in  a  smaller  threaded  block  hinged  to  the  outer  end  of 
the  larger  base  block,  extended  to  a  point  on  the  trunk  several  centi- 
meters below  and  formed  a  brace  which  kept  the  block  rigid  in  its  posi- 
tion with  respect  to  the  tree.  Flexible  supports  carried  a  floating 
frame  which  served  to  register  variations  in  thickness.  This  form  of 
base  was  heavy,  unwieldy,  and  by  reason  of  the  metal  was  subject  to 
temperature  variations  which  might  influence  the  record. 

1  Friedrich,  J.  Zuwachsautograph.  Centralb.  fQr  das  gesammte  Forstwesen.  31,  pp.  456- 
461.  Nov.  1905. 


10 


GROWTH   IN   TREES. 


as  a 


The  second  and  preferable  form  of  base  may  be  described  in  a  phrase 
belt  of  wooden  blocks  hinged  together.     Seasoned  and  oiled 


blocks  of  redwood  (Sequoia  sempervirens)  ,  15  by  7  by  7  cm.,  were 
bound  together  in  a  belt  by  pairs  of  galvanized  strips  of  iron.  Small 
bolts  passed  through  the  ends  of  these  strips  and  through  holes  near 


FIG.  1. — Earlier  form  of  dendrograph  with  which  all  records  previous  to  September  1920  were 
made.     This  instrument  takes  a  bearing  from  a  prepared  area  on  the  bark  of  the  tree  by  one  end 
of  a  email  lever,  the  other  end  of  which  is  connected  with  the  short  arm  of  a  recording  lever.     Th 
improved  instrument  includes  a  lever  set,  in  which  the  bearing  on  the  tree  is  made  by  a  hor 
zontally  moving  quartz  rod,  as  shown  in  fig.  2.     An  encircling  belt  of  wooden  blocks  serves  as 
base  and  support.     Flexible  wire  standards,  with  a  base  of  thin  sheet  metal,  are  clamped  i 
position  on  the  wooden  blocks,  and  screw  clamps  which  slide  up  and  down  on  the  wire  standarc 
serve  to  hold  the  floating  frame  in  a  horizontal  position.     The  entire  apparatus  is  so  adjusted  tha 
a  contact  rod  on  the  opposite  side  of  the  tree  ie  held  witfr  gentle  pressure  against  the  tree  and  any 
variation  in  diameter  is  then  expressed  by  movements  in  the  lever  set. 


GROWTH   IN   TREES.  11 

the  end  of  the  blocks  were  easily  put  in  place  or  removed,  so  that  any 
number  of  blocks  might  be  joined  to  form  a  support  which  would  en- 
circle a  tree  of  any  size.  From  4  to  9  blocks  were  used  in  most  of  the 
instruments.  A  wooden  block  of  larger  size,  carrying  an  upright  rod 
10  cm.  long  as  a  support  for  the  recorder,  was  used  to  close  the  support 
or  form  the  buckle  of  the  belt.  The  actual  fastening,  however,  con- 
sisted of  a  pair  of  threaded  rods  extending  from  the  large  block  and 
resting  in  the  slots  of  angle  irons  on  the  small  end  block.  Nuts  of 
suitable  form  could  be  turned  on  these  threaded  rods  until  a  suitable 
tension  had  been  put  on  the  belt  (see  fig.  1).  A  long  wooden  screw, 
working  in  a  small  block  hinged  to  the  outer  end  of  the  instrument  base, 
forms  a  supporting  brace  as  in  the  other  form  of  support.  When  such  a 
belt  base  is  drawn  tightly  about  a  tree  of  the  sizes  measured,  the  eight 
or  nine  blocks  used  adjust  themselves  to  the  irregularities  of  the  trunk, 
but  in  general  assume  a  tangential  position  and  press  tightly  on  the 
bark  and  cambium  internal  to  it,  but  the  total  disturbance  by  such  pres- 
sure is  small  and  does  not  affect  the  changes  in  the  volume  of  the  por- 
tions of  the  trunk  actually  measured,  a  few  centimeters  higher. 

The  essential  feature  of  the  apparatus  is  the  floating  frame  which 
makes  two  contacts  with  the  trunk.  One  such  contact  is  made  by  a 
set  screw,  carried  by  this  frame,  which  may  be  turned  to  a  point 
where  it  makes  a  slight  but  firm  contact  on  the  trunk.  The  second 
contact  is  made  by  the  quartz-bearing  rod  of  the  lever-set  carried  on 
the  floating  frame  at  a  point  diametrically  opposite  to  the  contact 
screw.  Any  change  of  the  trunk  affecting  the  distance  between  the 
end  of  the  contact  screw,  which  is  immovable  on  the  floating  frame, 
and  of  the  sliding  quartz  rod  of  the  lever  system  or  set  would  be  ex- 
pressed in  the  movement  of  the  pen  lever  which  traces  a  line  on  the 
graduated  paper  sheet  carried  by  the  revolving  cylinder. 

The  first  instruments  were  constructed  at  a  time,  during  the  Great 
War,  when  it  was  impossible  to  procure  the  alloys  which  have  a  low 
temperature  coefficient.  Floating  frames  of  wood  and  iron  were  con- 
structed in  a  U -shape.  The  curved  ends  of  the  U  consisted  of  a  bar 
of  wrought  iron,  1  by  ^  inches,  fastened  by  bolts  to  the  sides  of  the  U, 
which  were  of  seasoned  oak  boiled  in  paraffin.  The  oak  bars  used  for 
the  frames  of  the  carriage  tops  were  found  suitable  for  this  purpose  and 
(as  they  were  3  by  2  mm.  in  cross-section)  are  sufficiently  rigid.  The 
instrument  bar  was  a  strap  of  iron  with  the  ends  turned  at  right  angles 
to  be  parallel  to  the  wooden  bars.  These  short  arms  are  slotted  so 
that  the  instrument  bar  may  be  fixed  in  position  at  a  suitable  distance 
from  the  trunk.  Cold  would  cause  the  curved  iron  member  of  the 
frame  to  be  drawn  toward  the  tree,  and  as  the  turned  ends  of  the 
instrument  bars  run  from  the  tree  their  contraction  by  cold  would 
cause  a  movement  which  would  tend  to  maintain  an  equal  distance 
between  the  two  and  leave  uncompensated  only  the  temperature  varia- 


12  GROWTH   IN   TREES. 

tion  of  the  wooden  side  arms.  As  the  temperature  coefficient  of  such 
wood  is  about  0.000054,  or  3  times  as  great  as  that  of  brass,  extensive 
and  difficult  corrections  were  necessary. 

The  U-shaped  floating  frame  was  retained  during  the  earlier  stages 
of  development  of  the  dendrograph,  and  this  form  has  some  desirable 
features,  especially  when  the  record  of  a  slowly  growing  tree  is  to  be 
obtained  for  a  long  period.  Such  frames  have  now  been  used  in 
securing  records  of  growth  of  Pinus  radiata  No.  1  for  two  seasons; 
however,  the  enlargement  is  at  such  a  rapid  seasonal  rate  that  the 
frames  must  soon  be  replaced. 

The  final  form  of  the  floating  frame  is  that  of  a  polygon  constructed  of 
strips  or  bars  of  invar  or  bario,  15  to  30  cm.  in  length,  3  to  5  mm.  in 
thickness,  and  12  to  15  mm.  in  width.  These  pieces  have  slots  near 
each  end,  about  5  to  8  cm.  long,  through  which  short  bolts  are  passed. 
When  five  to  eight  such  strips  are  joined  to  form  a  suitable  frame  about 
a  tree,  the  nuts  on  these  bolts  are  tightened  and  the  joined  parts  are 
held  as  rigidly  as  of  one  piece.  One  of  the  members  of  the  floating 
frame  carries  a  block  of  metal  welded  to  it  and  bored  to  receive  the 
contact  screw  which  is  provided  with  a  set  nut.  The  member  of  the 
floating  frame  which  is  nearest  the  instrument  block  carrying  the 
recorder  is  bored  to  receive  the  small  bolts  which  carry  the  lever  set 
designed  especially  for  this  instrument. 

The  essential  feature  of  this  lever  set  is  a  quartz  rod,  3  or  4  mm.  in 
diameter,  7  or  8  cm.  in  length-,  which  slides  in  holes  of  the  vertical 
arms  of  the  adjustable  frame  of  the  set.  The  outer  end  of  this  rod 
is  fitted  with  a  slotted  cap  or  guide  by  which  its  rounded  end  is  kept 
in  place  against  the  short  arm  of  an  L-shaped  lever.  The  long  arm 
of  this  lever  carries  a  pen  of  the  type  used  on  thermographs.  The 
dropped  arms  of  the  frame  which  carry  the  sliding  quartz  rod  have 
three  pairs  of  holes,  so  that  the  rod  placed  in  the  lowermost  holes  en- 
gages the  short  arm  of  the  lever  near  its  end,  thus  causing  the  least 
amplification  of  its  movement  in  the  record,  which  is  ordinarily  about 
10  times.  The  rod  when  placed  in  the  middle  pair  of  holes  causes  the 
pen  to  move  through  an  arc  15  tunes  as  great  as  the  motion  of  the 
rod,  and  when  placed  in  the  uppermost  holes  the  bearing  against  the 
short  arm  of  the  lever  is  so  near  the  pivot  that  an  amplification  of  22 
is  made  in  the  record.  The  actual  amplification  is  of  course  tested  for 
each  instrument.  The  metal  parts  of  the  lever  set  are  of  monel,  since 
this  avoids  corrosion  and  the  construction  (as  shown  in  fig.  2)  is  such 
that  all  of  the  necessary  adjustments  are  made  possible  by  sliding  the 
parts  of  the  frame  upon  each  other 

The  recorder  is  also  of  a  design  perfected  for  use  with  this  instru- 
ment. A  strong  clockwork  is  inclosed  in  a  heavy  case.  The  upwardly 
projecting  end  of  the  msin  arbor  of  the  clock  is  fitted  with  a  cap  over- 
jutting  in  such  manner  that,  when  in  place,  water  coming  down  as 


GROWTH    IN    TREES. 


13 


rain  does  not  enter  the  case.  A  circular  table  or  base  is  fitted  to  the 
cap,  and  a  drum  made  of  a  pection  of  large  brass  pipe  sits  directly  on 
this  fitting  inside  its  raised  rim,  so  that  it  may  be  removed  without  dis- 
turbance of  the  clockwork. 

The  new  feature  of  importance  of  this  cylinder  is  the  manner  in 
which  the  record  paper  is  attached.     The  paper  is  80  mm.  in  width  and 


FIG.  2. — Improved  dendrograph  lever  set.  A,  inner  end  of  quarts  rod  in  contact  with  prepared 
surface  on  the  bark  of  the  tree.  The  outer  end  of  the  quartz  rod  is  fitted  with  a  metal  guide  which 
engages  the  short  arm  of  the  recording  lever  at  B.  The  long  arm  of  the  recording  lever,  D. 
carries  a  pen  which  makes  a  tracing  on  ruled  paper  on  a  revolving  drum.  The  horizontal  member 
of  the  frame  C,  which  carries  the  recording  lever,  may  be  toward  or  away  from  the  tree  to  adjust 
the  pen  at  any  point  on  the  paper  record  sheet. 

ruled  to  millimeters.  When  placed  on  the  drum  the  ends  are  thrust 
through  a  slot  1  mm.  in  width  and  the  free  ends  are  creased  on  the 
inside  without  further  fastening.  When  the  drum  with  the  paper  so 
attached  is  set  on  its  circular  base  the  paper  is  properly  in  position 
when  its  lower  edge  is  hi  contact  with  the  rim  of  the  base.  A  covering 
as  described  below  is  placed  over  the  recorder,  but  in  any  case  actual 
rain  falling  on  it  would  mar  only  the  record  and  could  not  damage  the 
instrument. 

The  floating  frame,  howrever,  is  exposed  to  all  features  of  the  weather 
and  to  the  effects  of  sunlight  which  might  cause  its  temperature  to 
vary  from  about  0°  C.  to  25°  C.  during  the  growing  season  of  the  trees 


14  GROWTH   IN   TREES. 

measured,  and  if  the  variations  were  to  be  recorded  during  the  entire 
year  the  range  would  be  even  greater.  The  change  in  dimensions  of  a 
floating  frame  of  invar  arranged  in  the  form  of  a  polygon  with  a  total 
perimeter  of  60  cm.  may  be  estimated  from  the  following  data.  The 
temperature  coefficient  of  this  metal  is  0.00000015  per  degree,  and  the 
daily  range  of  ah1  temperature  does  not  vary  beyond  25°  C.,  usually 
much  less.  The  daily  rise  in  temperature  of  this  yoke,  which  would 
tend  to  increase  its  radius  and  to  make  the  daily  shrinkage  of  the  tree 
appear  to  be  greater  than  it  really  is,  would  therefore  be  found  by 
the  following  formula: 

.,     V  (0.7  X  10  c)  600 


in  which  E  equals  expansion  and  V  the  range  of  variation.  E  there- 
fore is  equivalent  to  25  X  0.0000007  X  600  divided  by  3.1416.  The 
possible  enlargement  of  the  diameter  of  the  yoke,  if  the  temperature 
rose  from  10°  to  35°  C.,  which  would  be  a  maximum,  would  be  no  more 
than  0.0036  mm.  Part  of  this  is  practically  compensated  by  the 
radially  arranged  contact  screw  of  invar  which  projects  inwardly 
30  mm.  It  is  to  be  seen  that  when  this  error  is  amplified  12  tunes  it 
could  amount  to  no  more  than  about  0.04  mm.,  which  would  not  be  a 
discernible  interval  on  the  record.  The  use  of  invar  or  bario  may  be 
taken  to  furnish  a  floating  frame,  the  variation  of  which  would  be 
negligible  in  measurements  of  variations  in  the  trunks  of  trees. 

One  additional  feature  of  the  instrument  yet  remains  to  be  described, 
this  being  the  devices  by  which  the  floating  frame  is  kept  in  its  hori- 
zontal position  around  the  trunk.  This  is  accomplished  by  a  series 
of  clamps  and  upright  flexible  wire  supports.  Sections  of  bronze  wire 
or  bronze-coated  steel  wire,  about  10  cm.  in  length,  are  fastened  to  a 
foot  or  base  of  brass  3  by  5  cm.  Such  supports  are  placed  in  suitable 
positions  on  the  upper  surfaces  of  the  wooden  blocks  of  the  encircling 
belt  and  fastened  in  place  by  clamps  of  proper  size.  Each  upright 
wire  carries  a  small  brass  clamp  which  may  be  moved  up  and  down  and 
fastened  at  any  point.  The  free  end  of  this  clamp  is  slotted  to  receive 
the  flat  members  of  the  floating  frame  which  are  fixed  firmly  in  place 
by  set  screws.  Adjustments  of  positions  of  the  wire  supports  and  of 
the  clamps  on  the  members  of  the  floating  frame  are  made  until  the 
last  named  is  held  in  such  position  that  the  contact  screw  exerts  a 
small  amount  of  pressure  on  the  trunk,  so  that  any  variation  will  be 
expressed  by  movements  of  the  quartz  rod  of  the  lever  set  on  the  oppo- 
site side  of  the  tree. 

The  adjustment  of  the  contacts  is  a  matter  of  some  nicety.  A 
broad  chisel  may  be  used  to  slice  away  the  bark  until  a  thickness  of 
not  more  than  a  millimeter  remains  outside  of  the  living  tissue,  over  an 
area  about  equal  to  that  which  might  be  pressed  lightly  by  a  finger  tip. 


GROWTH    IN   TREES.  15 

Actual  adjustment  of  an  instrument  in  this  manner  is  a  work  of  about 
an  hour.  During  all  of  this  time  the  recording  lever  has  been  kept 
in  a  vertical  position.  It  is  now  lowered  until  the  short  arm  engages 
the  guide  on  the  quartz  rod  and  is  in  good  contact.  The  recorder  is 
now  swung  around  until  the  paper  on  the  drum  is  brought  against  the 
pen,  being  rotated  to  begin  tracing  on  the  proper  day  and  hour.  With 
pens  properly  inked,  a  complete  record- for  a  week  may  be  obtained 
without  further  attention. 

Not  all  of  the  results  cited  were  obtained  with  the  instrument  de- 
scribed above,  which  has  been  in  use  only  since  September  1920,  but 
the  earlier  records  have  not  been  used  in  any  manner  in  which  their 
faults  might  vitiate  the  general  discussions  and  conclusions  founded 
on  them. 

THE  DENDROMETER. 

The  records  made  by  the  dendrograph  show  the  volume  or  diameter 
of  the  tree  at  any  moment  and  the  variations  which  have  taken  place 
in  reaching  these  dimensions.  Such  observations  are  indispensable 
to  any  searching  study  of  the  course  and  physical  basis  of  the  growth 
procedure.  It  is  also  important  to  determine  the  total  amount  of 
growth  which  may  have  taken  place  in  a  trunk  during  a  season  or  a 
period  of  years.  Such  an  instrument  would  serve  to  check  the  detailed 
records  of  the  dendrograph  and  would  have  direct  usefulness  in  the  de- 
termination of  the  increment  in  trees  grown  for  timber. 

An  instrument  of  this  kind,  which  might  be  read  only  at  the  be- 
ginning or  end  of  a  season,  could  be  constructed  of  common  materials 
without  regard  to  the  temperature  coefficient  of  the  members.  Such 
an  instrument,  known  as  a  dendrometer,  was  designed  in  1920  and  a 
number  of  models  have  been  in  attachment  to  trees  since  May  of  that 
year.1 

The  principle  of  an  encircling  wire  carried  by  a  number  of  plungers, 
originally  tested  for  the  dendrograph  in  1918,  was  utilized  in  the 
construction  of  the  dendrometer.  Such  a  device  was  unsuitable  for 
the  recording  instrument,  as  it  was  impossible  to  secure  a  wire  of 
sufficient  flexibility  with  a  low  temperature  coefficient.  As  noted,  how- 
ever, this  objection  had  no  weight  in  the  simpler  instrument,  which 
was  to  be  read  at  long  intervals.  The  first  assembly  of  this  instru- 
ment, consisting  of  a  belt  of  blocks  linked  with  strips  of  galvanized 
iron  125  mm.  long,  40  mm.  wide,  and  0.8  mm.  in  thickness,  bearing 
guides  for  five  radially  arranged  plungers,  was  fastened  to  a  Quercus 

1  It  is  to  be  noted  that  the  term  dendrometer  has  been  applied  to  instruments  used  by  th« 
forester  by  which  the  diameter  of  trunks  is  taken  by  direct  observation,  the  observer  sighting  at 
the  part  of  the  trunk  to  be  measured.  See  D.  Bruce:  A  new  dendrometer,  Univ.  of  Calif.  Pub., 
3,  No.  4,  pp.  55-61,  1917. 


16  GROWTH    IN   TREES. 

agrifolia,  75  cm.  in  circumference,  on  May  28,  1920.  Spliced  banjo 
wires  of  silvered  steel  were  run  through  the  outer  ends  of  these  plungers 
or  contact  rods,  one  end  being  anchored  in  such  manner  that  slack 
could  be  taken  up  and  tension  adjusted;  the  other  end  was  taken  around 
a  small  pulley,  one  radius  of  which  was  prolonged  by  a  pointer  15  cm. 
long.  The  radius  of  the  pulley  was  0.5  mm.  Five  contact  points 
were  arranged  on  the  tree  which  would  allow  this  instrument  to  show 
variations  in  as  many  radii.  Six  months  later  the  tip  of  the  pointer 
had  moved  through  110  cm.  and  as  the  amplification  was  30,  the  actual 
enlargement  of  the  perimeter  of  the  polygon  made  by  the  wire  was 

-5-  cm.,  which  was  due  to  the  action  of  the  tree  in  5  radii.  This  elon- 
o 

gation  being  of  the  circumference,  the  average  elongation  of  a  radius 
would  be  represented  by 


iix^X 
3    X5  X 

This  would  imply  an  enlargement  of  a  millimeter  in  thickness.  It 
is  to  be  noted  that  the  observation  was  begun  at  a  time  when  the  tree 
had  made  the  greater  part  of  its  growth  for  the  season. 

After  a  series  of  trials  of  a  wide  variety  of  devices,  a  final  design  was 
adopted  in  which  the  support  was  a  narrow  band  of  galvanized  iron 
or  a  belt  of  heavy  wire  bent  in  undulating  folds,  the  ends  being  securely 
brought  together  by  slender  threaded  rods  working  in  slotted  angle- 
irons  attached  to  the  ends  of  the  belt.  Sections  of  copper  tubing  or 
copper  rods,  15  cm.,  long,  are  bent  into  the  form  of  an  L.  One  arm, 
10  cm.  long,  is  flattended  and  perforated  for  attachment  to  the  belt  or 
support.  The  other  arm  is  in  a  position  radial  to  the  tree  and  the 
spring-like  action  of  the  long  arm  presses  its  end  gently  against  a  pre- 
pared spot  in  the  bark.  A  pointer  and  dial  are  attached  to  the  support 
at  the  point  where  the  ends  are  brought  together.  One  end  of  a  piece 
of  nickel  wire,  about  28  or  30  gage,  is  anchored  to  a  post  on  the  dial, 
and  the  wire  is  led  around  the  tree,  passing  through  suitably  smoothed 
holes  in  the  short  arms  of  the  copper  arms  or  plungers,  and  the  free 
end  is  attached  to  the  short  arm  of  the  pointer  (fig.  3). 

Adjustment  of  either  end  of  the  wire  is  made  so  that  a  delicate  but 
positive  pressure  is  exerted  by  each  plunger  on  the  surface  of  the  trunk 
and  the  pointer  is  at  zero,  or  at  some  datum  point  duly  noted.  Such 
instruments  are  inexpensive,  so  that  they  might  be  used  in  large  num- 
bers in  any  serious  attempt  to  measure  increments  of  timber  trees,  and 
would  need  very  little  attention.  It  is  to  be  noted,  of  course,  that  they 
may  be  subject  to  accidents  from  falling  branches  or  large  animals;  or, 


GROWTH   IN   TREES. 


17 


if  the  wire  has  been  kinked  in  adjustment,  breaks  may  occur  after 
a  few  days  at  ordinary  tensions. 


FIG.  3. — One  form  of  the  dendrometer.  An  encircling  band  of  galvanized  steel  strip  is  brought 
together  at  B  and  rests  upon  wooden  blocks  bearing  on  the  bark  at  F,  F,  F,  F,  etc.  An  encircling 
wire  pasbes  through  suitable  holes  in  flexible  arms  attached  to  the  supporting  steel  strip.  This 
wire  is  anchored  to  a  post  on  the  inner  side  of  the  dial,  the  other  end  being  attached  to  the  short 
arm  of  the  indicator  at  A.  The  enlargement  which  has  taken  place  has  pressed  the  flexible  arms 
outward,  pulling  on  the  wire  to  such  extent  as  to  cause  the  indicator  point  to  move  from  zero  at 
the  bottom  of  the  scale  to  "4." 

MEASUREMENTS  OF  PINE  TREES. 

The  Monterey  pine  (Pinus  radiata)  is  native  to  the  maritime  climate 
of  the  fog  belt  of  the  Monterey  peninsula  and  the  slopes  of  the  Santa 
Lucia  mountains  to  the  southward ;  and,  as  numerous  trees  of  all  ages 
were  available  on  the  grounds  of  the  Coastal  Laboratory  at  Carmel,  it 
was  selected  for  an  intensive  study  of  the  growth  of  the  pines. 

This  tree  is  characterized  by  extremely  rapid  growth,  both  in  length 
and  thickness,  and  does  not  survive  to  an  age  of  more  than  about  80 
years.  The  staminate  and  pistillate  flowers  are  matured  late  in 
January  and  the  pollen  is  scattered  in  February.  Elongation  of  the 


18  GROWTH   IN  TREES. 

tips  of  the  branches,  especially  of  young  trees,  begins  about  this  time 
and  such  growth  may  continue  until  September,  according  to  Dr. 
Forrest  Shreve,1  who  reports  that  records  of  elongation  of  as  much  as 
10  feet  of  the  leaders  of  young  trees  are  in  existence.  Dr.  Shreve  has 
also  described  the  features  of  the  trunk,  but  an  example  examined  by 
the  author  will  serve  to  illustrate  the  structure  of  such  trunks.  This 
tree  was  about  12.5  meters  in  height,  15  cm.  in  diameter  a  meter  above 
the  ground,  and  had  12  layers  of  wood  in  the  heart  and  18  in  the  lighter- 
colored  sapwood.  The  heaviest  increments  to  the  trunk,  according 
to  Dr.  Shreve,  occur  in  the  period  of  development  between  10  and  20 
years  of  age,  at  which  time  very  heavy  layers  of  wood  may  be  formed. 

Dendrographic  measurements  of  the  variations  and  growth  of  jthe 
trunks  of  nine  trees  in  the  grounds  of  the  Coastal  Laboratory  have 
been  made  since  September  1918.  A  continuous  record  of  the  ba^al 
section  of  the  large  tree  upon  which  the  observations  were  begun  has 
been  kept  since  that  time,  and  a  second  instrument  was  attached  to 
this  tree  9  meters  above  the  ground  in  March  1920,  so  that  a  double 
record  for  an  entire  season  is  now  available. 

The  seasons  in  the  region  in  which  the  Monterey  pine  grows  are 
indeterminate  as  to  frost  and  temperature  features,  but  the  rainfall 
occurs  in  the  winter  and  growth  is  seen  to  depend  upon  the  soil  supply 
of  water  and  the  rising  temperatures,  with  the  result  that  enlargement 
of  the  trunks  continues  until  the  soil  moisture  around  the  absorbing 
roots  is  depleted  until  it  forms  no  more  than  6  to  10  per  cent  of  the  total 
weight. 

The  present  studies  have  been  devoted  chiefly  to  changes  in  volume 
of  trunks  and  so  many  technical  problems  have  been  encountered  that 
no  attention  has  been  paid  to  the  features  of  development  of  the  cam- 
bium inclusive  of  the  periods  of  cell-division,  of  xylem  formation,  of 
phloem  formation  and  collapse,  of  rifts  and  stresses  in  bark,  or  seasons 
of  activity  of  roots.  Important  contributions  on  these  subjects  have 
been  made  recently  by  L.  Knudson,2  H.  P.  Brown,3  and  I.  W.  Bailey.4 

It  was  thought  advisable,  however,  to  make  some  measurements  of 
the  changes  in  length  and  thickness  of  leaders  and  young  stems  and 
this  was  done  both  in  the  early  part  of  the  season  and  in  the  autumn. 

1  Shreve,  Forrest.     Stem  analysis  and  elongation  of  shoots  in  the  Monterey  pine.     Carnegie 
Inst.  Wash.  Year  Book  for  1919,  pp.  88  and  89. 

2  Knudson,  L.     Observations  on  the  inception,  season,  and  duration  of  cambium  development 
in  the  American  larch  (Larix  laricina  Du  Roi  Koch).     Bull.  Torr.  Bot.  Club,  40: 271-293,  June 
1913. 

3  Brown,  H.  P.     Growth  studies  in  forest  trees.     I.  Pinus  rigida  Mill.     Bot.  Gaz.,  54: 386-402, 
1912.     II.  Pinus  strobus  L.  same  journal,  59: 198-240,  1915. 

4  Bailey,  I.  W.     Phenomena  of  cell-division  in  the  cambium  of  arborescent  gymnooperms  and 
their  cytological  significance.     Proc.  Nat.  Acad.  Sci.,  5:  283-285,  1919. 

.     The  cambium  and  its  derivative  tissues.     II.  Size  variations  of  cambium  initials  in 

gymnosperms  and  angiosperms.  Amer.  Jour.  Bot.,  7:355-367,  1920.  III.  A  reconnaissance 
of  cytological  phenomena.  Amer.  Jour.  Bot.,  7:417-434,  1920. 


GROWTH   IN   TREES.  19 

The  daily  procedure  in  elongation  during  September  may  well  be 
illustrated  by  the  following  excerpts  from  the  notes: 

The  temperature  of  the  air  varied  between  13°  and  22°  C.  during  the  greater 
part  of  the  time,  this  equable  feature  of  the  climate  being  accompanied  by 
fogs  and  high  humidity. 

The  record  of  the  first  day  was  made  on  a  24-hour  clock  cylinder  to  give 
opportunity  for  minute  analysis.  This  showed  that  the  stem  contracted  as 
much  as  0.3  mm.  in  the  forenoon  period,  which  in  this  case  was  clear  and  sunny, 
and  in  the  periods  ending  the  next  morning  an  increase  of  12  mm.,  or  a  net 
total  of  8  mm.,  was  made.  This  behavior  was  duplicated  in  the  following  10 
days,  during  which  time  the  period  of  elongation  of  the  stem  came  to  a  close. 
Greater  activity  being  displayed  by  the  laterals,  attachment  was  transferred 
to  one  of  these  and  a  similar  procedure  was  recorded  for  7  days,  at  which  time 
it  also  came  to  a  state  approaching  quiescence  on  September  8. 

On  October  15  the  instrument  was  attached  to  the  lateral  of  another  plant 
continuously  in  the  shade  and  the  record  for  the  succeeding  20  days  shows 
daily  variation,  including  shortening  at  midday,  but  with  little  total  growth 
except  on  days  on  which  the  temperature  of  a  large  trunk  rose  to  17°  or  18°  C., 
or  the  air  was  humid  by  the  effect  of  fog  or  rain.  Such  a  case  was  produced  by 
fog  on  October  21  and  22,  which  were  followed  by  a  period  of  a  week  of  clear 
days  with  trunk  and  air  temperatures  not  widely  different  in  a  range  from  15° 
to  22°  C.  during  which  time  the  daily  variations  did  not  result  in  any  actual 
increase. 

The  influence  of  humidity  and  water  supply  is  illustrated  still  more  strikingly 
by  the  behavior  of  No.  5,  an  unbranched  plantlet  40  cm.  high,  probably  about 
16  months  old.  Attachment  was  made  to  the  tip  of  this  plant  on  September 
8  and  on  the  two  succeeding  days  a  midday  decrease  and  a  following  larger 
increase  of  0.5  mm.  or  less  were  displayed.  Beginning  at  midday  on  the 
llth,  rain  fell  continuously  for  50  hours  and  an  enormous  acceleration  ensued. 
The  temperature  during  this  time  was  19°  to  20°  C.  The  total  increase  during 
this  two-day  period  was  over  10  mm.,  which  was  5  or  6  times  the  previous  rate, 
in  cool,  dry  days  and  cooler  nights.  On  the  day  following  the  rain  the  increase 
fell  to  2.5  mm.,  after  which  the  daily  program  of  elongation  and  shrinkage 
followed,  with  a  net  increase,  however,  of  2.5  mm.  in  13  days,  the  rate  diminish- 
ing on  September  28,  at  the  end  of  this  period,  which  probably  soon  passed 
into  the  condition  already  described  for  No.  3.  This  record  illustrates 
markedly  the  accelerating  effect  of  humidity  on  growth  and  suggests  that 
warm  rainy  periods  of  even  a  few  day's  duration  may  have  a  permanent  effect 
on  the  structure  of  the  trunk. 

These  features  are  in  accordance  with  a  procedure  which  has  been  studied 
and  described  in  great  detail  in  a  large  number  of  morphological  types  of 
plants.  Excessive  or  maximum  water-loss  during  the  daylight  period  lessens 
the  rate  and  amount  of  enlargement  in  growing  stems  and  causes  fluctuations 
in  volume  of  quiescent  ones. 

It  is  to  be  noted  that  the  imbibitional  conditions  in  stems  a  year  old  are 
much  different  from  those  of  large  trunks.  Thus,  in  such  a  stem  the  epidermis 
is  still  unbroken,  the  cortex  is  chlorophyllose,  over  a  millimeter  in  thickness, 
and  the  numerous  long  leaves,  which  still  are  present,  may  withdraw  a  large 
amount  of  water.  The  growing  layer  is  nearly  as  thick  as  the  cortex,  while 
the  central  pith  is  3  or  4  mm.  in  diameter,  the  rays  through  the  wood  being 
much  in  evidence.  One-third  of  the  diameter  of  a  stem  24  mm.  in  thickness  is 
thus  made  up  of  thin-walled  cells  in  a  high  state  of  hydration  and  in  a  condition 
in  which  the  water  balance  of  the  system  may  be  quickly  modified  by  evapora- 
tion or  temperature  changes. 


20  GROWTH   IN   TREES. 

The  measurements  in  the  first  series  were  made  by  bringing  a  modified 
auxograph  lever  in  contact  with  the  upright  leader  of  a  young  pine  which  had 
been  surrounded  by  a  platform  and  held  rigidly  in  position.  The  net  gain  of 
the  daily  fluctuations  during  the  whole  of  August  amounted  to  nearly  a  milli- 
meter in  thickness.  .Now  ensued  a  period  of  high  fogs  which  during  3  days 
equalized  temperatures  and  humidity,  reducing  the  daily  variation,  but 
resulting  in  no  increase.  Finally,  on  September  5,  rising  temperatures  and 
humidity  had  the  effect  of  producing  a  net  gain  which  amounted  to  about  0.5 
mm.  before  a  rain  came  disarranging  the  clock-work  of  the  recording  cylinder. 
Two  days  after  this  rain  the  instrument  was  again  put  in  order  and  during 
the  following  2  weeks  a  daily  increase  in  diameter  was  recorded  which,  on 
September  27,  had  produced  a  net  thickening  of  about  2  mm.  The  regis- 
tration was  discontinued  for  2  weeks,  but  was  resumed  on  October  15.  The 
increase  had  evidently  continued  during  the  interval,  but  was  now  coming 
down  to  a  minimum,  as  the  net  thickening  in  the  following  2  weeks,  termi- 
nating October  29,  was  about  0.5  mm.1 

Further  observations  on  the  variations  of  young  stems  were  made  in 
the  autumn  of  1920.  A  small  tree,  No.  8,  8  or  9  years  old,  about 
3.5  meters  in  height,  was  bent  over  so  that  the  terminal  leader  which  had 
been  formed  by  the  growth  beginning  in  February  was  held  rigidly 
on  a  block  of  wood,  in  such  manner  that  the  vertical  swinging  aim  of 
an  auxograph  might  rest  directly  upon  it.  Another  tree,  No.  9,  5  years 
old,  about  2.7  meters  in  height,  was  similarly  arranged  but  with  the 
internode  formed  during  the  previous  year  under  measurement. 

The  record  of  No.  8  shows  that  enlargement  in  diameter  had  ceased 
on  September  17  and  that  progressive  shrinkage  was  recorded  during 
the  following  10  days.  Irrigation  was  followed  by  some  increase. 
The  daily  variation  was  not  so  great  in  the  older  internode  of  No.  9, 
and  irrigation  was  followed  by  a  more  pronounced  and  long-continued 
enlargement. 

The  auxographs  were  again  brought  into  bearing  at  the  same  places 
on  the  internodes  of  these  two  young  trees  for  10  days  beginning 
February  24,  1921.  The  terminal  internode  of  No.  8  was  now  nearly  a 
year  old  and  the  buds  at  its  tip  had  made  an  elongation  to  about  5  to 
10  cm.  during  the  previous  month.  The  internode  of  No.  9,  upon 
which  measurements  were  made,  was  now  nearly  2  years  old.  The 
buds  at  the  tip  of  the  terminal  internode  above  it  had  made  an  elonga- 
tion of  3  to  5  cm.  It  was  soon  seen  that  the  two-year-old  internode  of 
No,  9  had  not  awakened,  as  the  pen  traced  a  straight  line,  the  soil 
water  supply  being  sufficient  to  maintain  the  water  balance  in  the  wood. 
The  one-year-old  leader  of  No.  8  was  already  in  course  of  growth,  and 
during  the  10  days  of  the  record  showed  an  increase  of  0.8  mm.  in 
thickness.  A  slight  depression  of  the  rate  of  growth  occurred  in  the 
midday  period,  especially  on  days  of  highest  temperature. 

Passing  from  these  measurements  to  variations  in  pine  trunks,  more 
complex  conditions  are  encountered.  In  securing  dendrographic 

1  The  records  upon  which  the  above  statements   are  based    were   interpreted  erroneously, 
as  stated  in  my  account  of  1919.     See  Carnegie  Inst.  Wash.  Year  Book  for  1919,  p.  76. 


GROWTH    IN   TREES.  21 

measurements  the  old,  flaking  outer  cork  layers  of  the  bark  were  cut 
away  and  bearings  were  taken  on  the  thin  layer  formed  in  the  previous 
year,  which  had  not  yet  become  heavily  browned.  Internal  to  this  is 
the  bast,  which  forms  a  layer  about  2  mm.  in  thickness,  and  internal 
to  this  is  the  cambium  layer.  Growth  or  permanent  enlargement  would 
depend  upon  the  division,  enlargement,  and  differentiation  of  the 
elongated,  spindle-formed  elements  of  the  cambium. 

While  new  cells  are  being  formed  by  division,  and  these  are  under- 
going the  enlargement  constituting  one  of  the  main  features  of  growth, 
these  cells  form  a  very  thin  layer  external  to  the  woody  cylinder. 
This  woody  cylinder,  with  its  closed  systems  of  tracheids  or  wood- 
cells,  is  the  conducting  system  by  which  solutions  pars  from  the  roots 
to  the  transpiring  surfaces  of  the  leaves. 

The  rate  of  water-loss  from  the  leafy  surfaces  may  vary  widely 
during  the  course  of  the  day  as  a  result  of  changing  temperatures  of 
the  air,  while  the  temperature  at  which  water  passes  into  the  trunk  at 
its  base  changes  but  slowly,  and  chiefly  in  response  to  eoil-moisture 
proportions.  It  is  obvious  that  such  relations  between  absorption  and 
loss  of  water  may  result  in  more  water  being  given  off  during  any 
period  than  is  taken  in.  Such  excessive  transpiration  can,  of  course, 
occur  only  from  a  balance  or  surplus,  and  this  accumulated  reserve, 
occupying  the  entire  trunk  of  the  tree,  may  be  very  great.  Any 
lessening  of  its  volume,  however,  would  cause  variations  in  the  dimen- 
sions of  the  trunk  to  an  extent  determined  by  a  set  of  conditions  which 
need  not  be  elaborated  here. 

The  most  valuable  dendrographic  data,  so  far  available,  are  those 
obtained  from  the  Monterey  pine.  The  separate  trees,  five  in  number, 
to  which  dendrographs  have  been  attached  are  briefly  described  as 
below: 

No.  1  is  about  25  meters  in  height,  bearing  only  short,  thin  branches, 
with  the  trunk  40  to  44  cm.  in  diameter  a  meter  above  the  ground. 
Cores  taken  out  by  increment  borers  show  28  well-defined  layers  or 
"annual  rings."  The  radial  increment  the  first  year  was  14  mm.,  and 
varied  from  2  to  5  mm.  in  the  succeeding  ten  layers,  which  may  not 
safely  be  taken  to  represent  annual  formations.  The  second  series  of 
ten  layers  has  a  total  thickness  of  62  mm.,  the  separate  layers  varying 
from  2  to  10  mm.,  the  thinner  ones  being  in  all  probability  formed  as 
the  result  of  autumnal  rains,  such  as  occurred  in  1918.  The  total  of 
the  11  outermost  layers  amounts  to  60  mm.  of  radial  thickness,  varying 
from  2  to  9  mm.  in  the  separate  layers.  Thus,  on  the  basis  of  experience 
described  below,  by  which  the  tree  after  having  formed  a  layer  5  mm. 
in  thickness  in  the  early  part  of  1920  was  awakened  to  form  a  second 
layer  of  equal  thickness  by  irrigation,  it  is  assumed  that  the  layer  2  mm. 
thick  interior  to  the  layer  of  1919,  which  is  8  mm.  in  thickness,  resulted 
from  a  rainfall  of  5  inches  early  in  September  1918.  Formation  of  a 


22  GROWTH   IN   TREES. 

layer  3  mm.  in  thickness  had  taken  place  during  the  first  half  of  the 
season  in  that  year.  Of  the  31  layers  or  rings  of  this  tree,  one  'was 
added  by  irrigation  in  1920,  one  has  the  appearance  of  resulting  from 
autumnal  rains  in  1918,  one  very  thin  one  was  probably  formed  under 
such  circumstances  in  1907,  and  another  in  1904.  The  tree  may 
therefore  be  considered  as  being  27  years  old  at  the  beginning  of  the 
season  of  1921. 

During  1920  a  second  instrument  was  placed  on  the  trunk,  8  meters 
above  the  ground.  Tree  No.  2  of  this  species  was  about  18  meters  in 
height  and  40  cm.  in  diameter  near  the  base,  with  heavier  branches 
than  No.  1,  and  stood  on  a  sandy  slope  facing  northward.  A  wide 
variety  of  devices  was  tested  on  the  instruments  attached  to  this  tree, 
so  that  no  continuous  record,  such  as  that  which  has  been  obtained 
from  No.  1,  was  obtained. 

Monterey  pine  No.  6  was  the  smallest  tree  of  this  species  to  which  the 
dendrograph  with  floating  frame  was  applied.  It  was  about  10  meters 
in  height,  16  cm.  in  diameter  near  the  ground,  and  stood  on  a  north- 
facing  slope  in  position  where  the  direct  sunlight  did  not  strike  the 
ground,  which  therefore  remained  at  a  lower  temperature  and  with  a 
higher  moisture  content  than  the  other  trees.  The  presence  of  20 
rings  or  layers  indicated  an  age  of  17  years.  The  layer  formed  in  1920 
had  a  thickness  of  3  mm.,  which  was  equivalent  to  that  of  1919,  and 
the  secondary  layers  of  1907  and  1904  were  plainly  apparent. 

No.  7  was  about  14  meters  in  height  and  35  cm.  in  diameter  near  the 
base.  Observations  on  this  tree  were  confined  to  dendrographic 
measurements  of  the  woody  cylinder  from  bearings  made  at  the  bottom 
of  borings  extending  through  the  wood  of  the  previous  year.  Tem- 
peratures of  the  outer  layer  of  the  trunk  and  of  the  heart  were  also 
taken  by  mercurial  thermometers.  This  tree  stood  on  a  north-facing 
slope  of  a  "fog  channel"  near  No.  6,  which  was  exposed  to  similar 
conditions. 

The  most  obvious  points  of  interest  in  the  growth  program  of  each 
year  are  those  which  concern  the  dates  of  awakening  and  cessation  of 
growth  of  terminals  and  of  the  trunk. 

Elongation  of  terminals  of  No.  1  began  early  in  February  1919,  but 
no  enlargment  of  the  trunk  was  measurable  until  March  30.  A 
period  of  low  relative  humidity  and  high  temperature  resulted  in  no 
increase  in  diameter  of  the  trunk  between  May  29  and  June  6,  after 
which  enlargement  took  place  at  a  low  rate  for  a  few  days,  alternating 
with  periods  in  which  only  reversible  variations  were  discernible. 
This  later  phase  of  growth  might  be  identifiable  with  an  after  develop- 
ment of  phloem,  such  as  has  been  described  by  Brown1  in  Pinus 
strobus.  The  total  net  accretion  on  the  diameter  measured  by  the  den- 

1  Brown,  H.  P.     Growth  studies  of  forest  trees.     Bot.  Gaz.,  59:237.     1915. 


GEOWTH   IN   TREES.  23 

drograph  was  9  mm.  and  the  thickness  of  this  layer  (laid  down  in  1919) 
taken  from  a  boring  on  another  diameter,  in  January  1921,  was  about 
8  mm. 

Heavy  rains  beginning  on  November  26,  1919,  were  followed  by  an 
increase  beginning  on  November  29,  which  continued  until  De- 
cember 14.  A  similar  slight  increase  following  rain  took  place  early 
in  January  and  late  in  January. 

The  instrument  was  reset  on  February  9,  1920,  and  a  second  one 
reached  by  a  scaffolding  attached  at  a  point  8  meters  above  it,  both 
making  a  record  in  which  the  variations  in  diameter  were  amplified 
8  times  (see  fig.  4).  The  circumference  of  the  trunk  at  the  upper  in- 
strument was  100  cm.  as  compared  with  130  cm.  at  the  lower  one. 
The  levers  of  both  instruments  were  set  to  give  an  amplification  of 
8  times,  so  that  it  was  possible  to  make  direct  comparisons  of  the  ac- 
tion of  the  trunk  in  the  two  places.  The  bark  in  both  cases  was  thinned 
so  that  the  contacts  were  made  on  layers  of  cork  not  more  than  a 
millimeter  in  thickness.  The  bark  at  the  base  of  the  tree  was  heavy 
and  was  coming  away  in  flakes,  while  that  at  the  upper  instrument 
had  begun  to  show  only  shallow  rifts  and  was  not  more  than  3  or 
4  mm.  thick  at  any  place.  Thermometers  thrust  under  the  bark  on 
the  north  side  of  the  trunk  showed  temperatures  as  low  as  6°  C.  on  the 
date  mentioned  and  as  low  as  8°  C.  on  March  30. 

Some  enlargement  of  the  same  type  followed  rain  March  18  to  22, 
but  this  was  followed  by  a  period  of  reversing  variations,  and  not  until 
April  7  did  a  continuing  enlargement  begin  which  showed  an  initial 
rate  slightly  greater  than  that  at  the  uppermost  instrument,  which 
began  on  the  same  day  (fig.  5). 

As  this  manuscript  is  being  completed,  the  records  for  the  early 
part  of  1921  are  available.  They  show  that  the  tips  of  the  branches 
on  young  and  old  trees  began  to  grow  about  mid-January,  and  that  the 
enlargement  of  the  upper  part  of  the  trunk  of  this  tree  showed  en- 
largement on  the  27th  of  January,  2  days  earlier  than  any  increase 
of  the  lower  part  of  the  trunk.  Action  in  the  two  places  was  syn- 
chronous in  1920,  but  did  not  begin  until  2  months  later  than  the 
awakening  of  the  tips  of  the  branches.  No  attempt  has  yet  been 
made  to  correlate  these  facts  with  the  activities  of  the  roots,  but  the 
observations  of  W.  B.  McDougall  are  to  the  effect  that  growth  of  the 
roots  begins  quite  early  in  the  season  and  that  it  depends  largely  upon 
moisture  and  temperature.1 

As  in  the  previous  year,  a  period  of  reversible  variations  began  late 
in  May  1920,  which  continued  until  July  2,  at  which  time  the  soil 
moisture  content  had  come  down  to  5  to  7  per  cent.  The  total  accre- 
tion at  the  base  of  the  tree  was  slightly  less  than  3  mm.,  slightly 

1  McDougall,  W.  B.    The  growth  of  forest  tree  roots.     Amer.  Jour.  Bot.,  3:385-392.    1910. 


GROWTH   IN   TREES. 


FIG.  4. — Monterey  pine  No.  1,  with  dendrographs  attached  near  the  ground  and  at 
a  height  of  9  meters. 


GROWTH   IN   TREES. 


25 


greater  than  2  mm.  at  the  upper  instrument,  differences  which  might 
be  seen  in  comparison  of  different  diameters  at  any  part  of  the  trunk. 
This  layer  showed  a  thickness  of  4  mm.  in  the  boring  on  a  different 
radius,  on  the  lower  and  upper  part  of  the  trunk. 

A  number  of  tile  pipes  were  now  sunk  in  the  soil  in  an  area  around  the 
tree,  so  that  water  might  be  conducted  to  the  absorbing  roots  and  3,000 
gallons  of  water  were  poured  into  these  holes  on  July  1,  1920,  with  the 
result  that  an  enlargement  was  visible  a  day  later,  which  was  slightly 


MAY  3  1920 


FIG.  5. — Dendrographic  records  of  the  changes  in  the  trunk  of  a  Monterey  pine  made  by  the  two 
instruments  attached  to  No.  1,  as  in  fig.  4.  Record  A  is  from  Ihe  lower  part  of  the  trunk  and  B 
from  the  higher  point,  for  the  week  beginning  May  3,  1920.  The  sheet  is  marked  into  6-hour 
periods  and  the  spaces  represent  10  mm.;  the  actual  changes  in  the  trunk  being  X  8.  Enlarge- 
ment and  partially  equalizing  daily  variations  are  displayed. 


28    1320 


JUNE    28   1920 


— 

_  — 

•~—  - 

—  - 

' 

^ 

gois 

wule 
ive 

Xo  S 

A  m 

jrmr 

ft 

FIG.  6. — Equalizing  daily  variations  of  trunk  of  Monterey  pine  No.  1  for  week  beginning  June 
28, 1920.  Application  of  water  to  soil  around  roots  after  6  p.  m.  on  July  2  was  followed  by  upward 
course  of  record  lines  from  both  instruments.  Variations  X  8  on  10  mm.  scale. 

greater  at  the  lower  instrument  (fig.  6).  Additional  water  was  given 
on  each  of  the  2  days  following,  and  enlargement  continued  at  the  upper 
instrument  until  about  August  16.  During  this  period  of  16  days  an 
enlargement  of  2  mm.  in  diameter  had  taken  place  at  the  upper 
instrument,  9  meters  above  the  ground,  and  of  4  mm.  at  the  lower 
instrument,  1  meter  above  the  ground  (fig.  7).  Enlargement  at  the 
base  continued  until  September  15,  at  which  time  a  further  thick- 
ening of  2  mm.  had  taken  place,  making  a  total  thickening  of  9  mm. 
at  the  base.  Both  measurements  were  in  agreement  with  borings 
taken  in  January  and  February  1921.  Then  followed  a  month  of 


26 


GROWTH   IN   TREES. 


reversible  variations  with  some  slight  increases  on  both  places  on  the 
trunk  following  a  rain  on  October  14.  Again  some  increases  occurred, 
beginning  on  November  16.  Similar  period  of  increase  occurred  in 
December.  No  actual  seasonal  or  winter  shrinkages  of  the  stem  at 
either  point  could  be  detected. 

Very  interesting  occurrences  of  this  sort,  however,  were  observed  in 
connection  with  rains.  On  April  15-16,  December  21-23,  30-31, 
a  continuous  enlargement  of  the  trunk  took  place  which  would  be 
wholly  or  almost  wholly  lost  on  the  sunny  day  following. 


AUG.   16  1920 


8) 
•» 

H 
0  — 

B 

M 

g 

M. 

tiA 

M 

•  —  f 

-  

~~^ 

.  *-" 

^—  — 

—  s, 

"~N, 

.  

—  f 

n 

v 

X^x 

•""* 

s 

•  —  • 

s^ 

'  —  " 

^_ 

FIG.  7. — Dendrographic  record  of  the  variations  of  lower  and  upper  parts  of  trunk  of  Monterey 
pine  No.  1  at  end  of  period  affected  by  irrigation. 

The  present  record  is  closed  on  January  27,  1921,  at  which  time  the 
staminate  flowers  were  nearly  mature  and  the  terminal  buds  were 
beginning  to  swell,  and  some  actual  enlargement  of  the  trunk  had 
begun  and  was  still  in  progress  on  January  31. 

During  1920  the  basal  part  of  the  trunk  had  shown  a  total  enlarge- 
ment of  nearly  9  mm.  in  diameter,  and  the  section  8  meters  from  the 
ground  about  6  mm.  The  accretion  of  1920  appeared  in  borings  at  the 
base  of  the  tree  as  two  layers  in  two  cores  5  and  4  mm.  in  thickness, 
when  measured  at  the  end  of  January  1921.  The  outer  layer  may  be 
taken  as  representing  accretion  following  irrigation,  which,  it  may  be 
suggested,  may  have  been  largely  in  the  phloem.  The  borings  at  the 
higher  point  snowed  two  layers,  4  and  2  mm.  in  thickness. 

Awakening  of  buds  took  place  several  weeks  before  enlargement  of 
the  trunk  began  in  1919  and  1920,  but  in  1921  growth  of  both  kinds 
was  apparent  the  last  week  in  January,  nearly  two  months  earlier  than 
the  observed  dates  of  enlargement  of  trunks  in  previous  years. 

The  variations  of  a  younger  tree  were  sought  by  the  attachment  of 
an  instrument  to  Monterey  pine  No.  6  on  February  12,  1920.  This 
tree  may  be  identified  as  beginning  in  1904,  as  it  made  a  second  layer 
of  wood  in  its  first  year  and  shows  the  extra  formations  in  1907  and 
1918.  The  floating  frame  of  the  instrument  was  of  invar,  the  levers 
being  set  at  first  to  amplify  5  and  later  to  15  times.  The  trunk  had  a 
diameter  of  18  cm.  and  the  first  discernible  enlargement  was  on 


GROWTH    IN   TREES. 


27 


March  16,  after  which  acceleration  carried  growth  to  a  maximum  rate 
in  the  last  10  days  of  April.  The  rate  now  slackened  and  growth 
ceased  about  June  1,  with  a  total  increase  of  4.5  mm.  in  diameter. 

A  rain  on  June  14  was  followed  by  some  growth  in  the  following 
week,  after  a  period  of  reversible  alterations  ensued.  Not  until  late 
in  July  did  a  slight  enlargement  recur  and  a  similar  impulse  was  re- 
corded at  the  end  of  August  (fig.  8).  No  further  increase  could  be 
detected,  but  a  shrinkage  began  on  October  11  which  continued  until 


FIG.  8. — Dendrographic  records  of  Monterey  pine  No.  6,  with  no  growth  in  week  of  March  1, 
1920,  beginning  growth  in  week  of  March  22-29,  vigorous  enlargement  in  week  April  12-19  daily 
equalizing  variations  of  wide  amplitude  in  week  of  June  28-July  5,  and  reduced  variations  late  in 
September.  Variations  X  5  on  scale  of  10  mm.  intervals. 

the  instrument  was  dismounted  a  week  later.  A  total  increase  of 
5  mm.  had  been  recorded.  It  is  to  be  noted  that  the  terminals  and 
tips  of  the  branches  had  made  a  growth  of  several  centimeters  when 
the  observations  were  begun,  and  that  such  elongation  must  have 
started  about  two  months  prior  to  the  increase  in  the  trunk. 

Measurement  of  another  pine  (Pinus  chihuahuana) ,  on  the  slopes 
of  the  Santa  Catalina  mountains,  an  isolated  range  near  the  Desert 
Laboratory,  gave  a  set  of  results  under  conditions  different  from  those 
afforded  by  the  indeterminate  seasons  of  the  coastal  climate.  A  tree 
40  cm.  in  diameter,  in  the  lower  edge  of  the  pine  belt  at  about  2,000 
meters,  was  selected  for  observation.  This  location  is  characterized 
by  a  coarse  granitic  soil,  winter  and  mid-summer  rainfall;  minimum 
air  temperatures  of  8°  C.  and  summer  maxima  of  40°  C.  are  of  record. 


28 


GROWTH   IN  TREES. 


This  tree  stood  about  4  miles  from  the  base  of  the  mountain  and  the 
instrument  was  transported  this  distance  by  pack  animals  and  put  in 
action  on  April  4,  1918,  being  visited  weekly  until  the  end  of  October. 
The  record  showed  some  enlargement,  beginning  April  14,  with  a 
cambium  temperature  of  13°  C.,  with  readings  as  high  as  28°  C.  in  the 
following  10  days.  When  observations  were  taken  on  April  23,  the 
temperature  of  the  cambium  was  10°  C.  and  enlargement  had  ceased. 
A  slight  swelling  occurred  May  13-20.  On  May  22  a  shrinkage  began 


13   1919 


MAY    28    1919 


FIG.  9.— Dendrographic  records  of  Chihuahua  pine,  with  variations  X  5  on  10  mm.  intervals. 
Some  enlargement  shown  in  week  beginning  April  15,  1919;  shrinkage  during  week  beginning 
May  20;  enlargement  in  week  beginning  May  28;  daily  equalizing  variations  of  wide  amplitude 
in  week  beginning  June  13 ;  reduced  variations  and  shrinkage  in  week  beginning  July  11 ;  increased 
variations  and  actual  increases  in  diameter  in  week  beginning  August  16,  and  reduced  daily 
variations  in  late  October. 

which  in  6  days  amounted  to  1  nun.,  or  half  the  total  increase  during 
the  previous  two  months.  Increase  began  on  May  28,  which  amounted 
to  about  2  mm.  on  June  14,  at  which  time  equalizing  variations  began 
at  tree  temperatures  of  23°  to  27°  C.,  which  continued  until  June  28. 
Now,  in  the  extreme  hot  mid-summer,  shrinkage  began  which  con- 
tinued until  July  20,  or  until  about  3  weeks  after  the  summer  rains 
began.  During  this  time  a  shrinkage  of  about  2  mm.  had  ensued, 
which  was  equivalent  to  about  three-fourths  of  the  gain  up  to  this 
date.  A  period  of  increase,  ending  August  23,  resulted  in  a  gain  of 


GROWTH    IN    TREES.  29 

5  mm.,  of  which  nearly  one-half  was  lost  in  the  last  week  of  August. 
Another  slight  swelling  began  September  14,  terminating  October  5, 
after  which  equalizing  daily  variations  occurred  until  the  instrument 
was  dismounted  October  221  (fig.  9). 

The  total  enlargements  amounted  to  about  10  mm.  and  the  total 
shrinkage  during  the  season  to  about-  5  mm.  It  is  obvious  that  the 
woody  layers  formed  in  such  an  interrupted  cycle  of  growth  must  be 
difficult  of  interpretation  by  the  observers  who  seek  to  obtain  the 
history  of  the  tree  from  its  "annual  rings."  Dr.  Shreve  has  found 
that  individuals  of  this  species  form  two  such  rings  in  locations  at 
slightly  greater  altitude  but  similar  climatic  conditions.2 

A  dendrograph  was  attached  to  a  yellow-pine  tree  (Pinus  scopulorwri) 
at  the  Fort  Valley  Forest  Experiment  Station  near  Flagstaff,  Arizona, 
late  in  April  1920.  This  tree  was  about  45  cm.  in  diameter  and  had 
apparently  ceased  growth  or  was  quiescent  during  this  season.  No 
permanent  change  in  diameter  amounting  to  as  much  as  a  millimeter 
occurred  during  the  summer.  Equalizing  variations  were  marked, 
however,  during  the  latter  half  of  July,  after  which  the  record  showed 
but  little  variation.  Mr.  G.  A.  Pearson,  in  charge  of  the  Experiment 
Station,  reports  that  this  tree  showed  some  growth  of  branches  and 
terminals  in  192 1.3 

A  dendrograph  was  installed  on  the  basal  section  of  a  yellow  pine 
(Pinus  ponderosa)  at  the  Alpine  Laboratory,  which  made  a  record 
from  June  5  to  September  15,  1920.  Mr.  Loftfield,  who  was  in  charge 
of  the  instrument,  reports  that  this  tree  was  nearly  36  cm.  in  diameter 
and  that  it  stood  on  an  east-southeast  slope  near  the  Douglas  fir  which 
was  also  measured.  Thermographic  and  hygrographic  records  were 
obtained  which  pertain  to  both  trees.  As  the  instrument  was  set  to 
amplify  15  times,  the  daily  equalizing  variations  appeared  very  marked 
at  the  beginning,  amounting  to  as  much  as  0.5  mm.  in  diameter  daily. 
An  increase  in  diameter  was  noticeable  on  June  14,  on  which  date  an 
inch  of  rainfall  was  noted,  but  this  was  only  a  temporary  increase,  as 
equalization  followed.  A  week  later  the  buds  awoke  and  disturbances 
of  the  daily  variation  ensued.  The  branches  reached  full  length  early 
in  July  and  the  leaves  full  size  by  the  middle  of  the  month,  but  not 
until  a  month  later  (August  12),  in  a  period  of  heavy  rains,  did  an 
increase  take  place.  This  continued  until  September  4,  and  during 
this  period  of  23  days  a  net  enlargement  of  nearly  2  mm.  in  diameter  had 
taken  place,  after  which  some  shrinkage  accompanied  the  daily 

1  The  above  statements  are  to  be  taken  in  correction  of  the  preliminary  notice  on  the  growth  of 
the  Chihuahua  pine  in  Carnegie  Inst.  Wash.  Year  Book  for  1918,  p.  75. 

2  Shreve,  F.     The  density  of  stand  and  rate  of  growth  of  Arizona  yellow  pine  as  influenced  by 
climatic  conditions.     Jour.  Forestry,  15:695-707.     Oct.  1917. 

3  Pearson,  G.  A.     The  relation  between  spring  precipitation  and  height-growth  of  western 
yellow  pine  saplings  in  Arizona.     Jour.  Forestry,  16:  677-689.     1918.     Boerker,  R.  H.     Rela- 
tion between  height-growth  of  larch  seedlings  and  weather  conditions.    Jour.  Forestry,  16:861- 
870.     Dec.  1918. 


30  GROWTH   IN   TREES. 

variations.  The  effects  of  humidity  and  temperature  will  be  presented 
in  a  later  section.  A  core,  taken  from  this  tree  by  Dr.  A.  E.  Douglass, 
showed  74  layers  or  rings  which  varied  from  1  to  5  mm.  in  thickness, 
that  for  1918  and  for  1919  being  about  the  same  thickness  as  the 
measurement  for  1920  just  given. 

MEASUREMENTS  OF  A  SPRUCE  AND  A  FIR. 

The  Douglas  fir  (Pseudotsuga  taxifolid),  at  the  Alpine  Labora- 
tory on  the  slopes  of  Pikes  Peak  to  which  the  dendrograph  was 
attached,  was  nearly  36  cm.  in  diameter  and  the  instrument  had 
an  amplification  of  nearly  16  times.  The  buds  were  developing 
rapidly  when  observations  were  begun  on  June  17,  at  which  time  in- 
crease of  the  diameter  of  the  trunk  was  visible  in  the  daily  variations. 
Growth  was  already  in  progress.  The  increase  continued  at  a  low 
rate  until  July  21,  at  which  time  a  total  gain  of  2  mm.  in  diameter 
had  been  made.  After  some  days  of  equalizing  variations,  with 
temporary  swellings  consequent  upon  rains,  an  increase  began  August 
11,  which  continued  until  the  22d,  making  the  total  accretion  for  the 
season  2.6  mm.  The  shrinkage  which  ensued  during  the  first  half  of 
September  reduced  this  total  to  2  mm. 

The  only  continuous  record  of  the  growth  of  this  tree  which  had  been 
made  previously  is  that  by  Mr.  A.  Mallock,  who  measured  variations 
in  the  girth  of  a  tree  which  had  a  circumference  of  33^  inches,  by 
means  of  an  invar  tape  connected  with  glass  prisms  arranged  to  observe 
movements  of  interference  bands.  These  observations  were  made 
July  5  to  July  16,  1917,  in  England.  It  is  not  known  whether  any 
growth  had  taken  place  earlier  in  the  season,  but  a  shrinkage  was  in 
progress  during  the  first  3  days  of  the  observations,  after  which  en- 
largement began,  and  continued  at  a  varying  rate  during  the  next  8 
days.  Slackening  in  the  rate  of  growth  occurred  during  the  midday 
period,  and  the  increase  was  most  rapid  at  night  and  following  rains.1 

The  actual  beginning  of  growth  of  the  trunk  was  not  observed,  but 
probably  not  much  had  taken  place  before  the  record  began,  as  the 
buds  were  just  opening.  The  record  of  this  fir  is  to  be  compared  with 
that  of  a  blue  spruce  (Picea  pungens),  which  was  measured  by  an 
instrument  in  the  hands  of  Mr.  C.  F.  Korstian.  This  tree  is  on  the 
Cottonwood  nursery  grounds,  25  miles  southeast  of  Salt  Lake  City,  at 
an  elevation  of  about  2,250  meters.  This  tree  was  38  cm.  in  diameter 
and  enlargement  was  in  progress  and  the  buds  were  opening  on  June  7. 
The  course  of  growth  was  similar  to  that  of  the  Douglas  fir,  and  as  it  is 
being  described  in  an  article  by  Mr.  Korstian,  in  the  Botanical 
Gazette  for  June  1921,  it  will  not  be  repeated  here. 

1  Mallock,  A.  Growth  of  trees,  with  a  note  on  interference  bands  formed  by  rays  at  small 
angles.  Proc.  Roy.  Soc.,  96  B  (see  especially  p.  193),  1919. 


GROWTH   IN   TREES.  31 

GROWTH  OF  THE  CALIFORNIA  LIVE  OAK. 

The  California  live  oak  (Quercus  agrifolia'),  which  is*  one  of  the 
commonest  of  the  oaks  of  the  Pacific  slope  and  in  the  region  of  the 
Coastal  Laboratory,  is  a  small  tree  with  trunks  25  to  50  cm.  in  diameter. 
The  leaves  of  one  season  remain  on  the  tree  until  those  of  the  next 
season  are  unfolding,  which  in  this  region  begins  early  in  February. 
The  first  indication  of  awakening  activity  is  the  elongation  of  the 
leafy  branches  which  may  occur  in  some  individuals  2  or  3  weeks  earlier 
than  in  others  a  short  distance  away.  As  will  be  seen  from  the  records 
discussed  below,  enlargement  of  the  trunk  began  in  March,  somewhat 
earlier  than  in  the  Monterey  pine  in  the  same  locality. 

Measurement  of  this  species  includes  one  feature  widely  different 
from  the  pines,  in  that  the  bark  remains  alive  and  turgid  until  it 
reaches  a  thickness  as  much  as  5  cm.,  and  it  is  upon  the  surface  of  this 
structure  that  dendrographic  bearings  must  be  taken.  The  bark 
finally  becomes  deeply  and  irregularly  furrowed,  so  that  any  single 
line  around  a  tree  may  cross  not  more  than  three  or  four  of  such 
rifts,  which  appear  to  go  nearly  to  the  wood,  a  condition  which  was 
found  in  the  first  tree  measured. 

A  dendrograph  with  a  floating  frame  of  bario  in  the  shape  of  a  large 
U  was  mounted  on  a  rectangular  frame  support  and  put  in  place  on 
No.  1  of  this  tree  on  February  17,  1919.  On  March  1  a  slight  increase 
was  recorded,  but  not  until  March  11  did  positive  growth  begin  and 
this  continued  until  the  end  of  May.  Temperatures  (1  cm.  interior  to 
the  surface  of  the  bark)  of  7°  to  9°  C.  were  recorded  during  February 
and  March,  rising  to  14°  C.  during  the  growing  period.  Later  in  the 
summer  records  of  18°  C.  were  taken. 

Continuous  records  were  kept  and  on  February  10,  1920,  the  instru- 
ment was  changed  to  one  using  a  belt  of  blocks  as  a  support  for  the 
floating  frame  of  bario.  No  growth  of  the  tips  of  the  branches  had 
yet  taken  place  and  temperatures  as  low  as  6°  C.  were  noted  on  several 
mornings.  One  record  of  9°  C.  was  taken  as  late  as  March  30  in  the 
growing  season. 

The  daily  variations  in  this  type  of  tree  are  very  slight,  so  that  the 
record  did  not  vary  widely  from  a  level  line  until  March  10,  when  it 
began  to  take  an  upward  course  which  was  not  slackened  until  after 
May  5.  Growth  was  again  actively  in  progress  by  the  18th,  to  slow 
down  again  by  the  28th,  a  shrinkage  of  marked  character  taking  place 
during  the  following  week,  followed  by  quiescence. 

Growth  was  resumed  on  June  18,  but  soon  ceased.  Another  impulse 
between  June  22-28,  another  September  25-28,  were  observable.  A 
decided  shrinkage  began  on  September  30,  which  continued  for  7  days. 
An  increase  took  place  during  the  last  10  days  in  October,  and  a  very 
marked  shrinkage  began  December  1,  which  continued,  with  some 


32 


GROWTH   IN   TREES. 


interruptions,  until  about  January  18,  1920.  The  total  accretions 
amounted  to  about  5  mm.  in  diameter,  of  which  some  was  lost  by  the 
shrinkage  described.1 

Changes  in  size  consequent  upon  rains  followed  until  the  instrument 
was  replaced  on  February  9,  1920,  by  a  model  using  the  belts  of  blocks 
for  a  base,  but  retaining  the  U-shaped  floating  frame  of  bario.  New 
shoots  5  to  8  cm.  long  and  leaves  one-third  full  size  were  noted  on 
March  15,  but  no  enlargement  of  the  trunk  had  yet  occurred.  Actual 
enlargement  did  not  begin  until  April  9,  one  month  later  than  in  the 
previous  year. 

The  instrument  was  jammed  for  2  weeks,  but  when  set  in  order 
showed  continued  action,  justifying  an  estimate  of  the  accretion  not 
recorded.  Growth  at  a  decreasing  rate  continued  until  August  1,  at 
which  time  a  total  increase  of  4.6  mm.  had  ensued.  After  this  time 
the  record  varied  but  little  from  a  level  line  and  the  instrument  was 
dismounted  on  September  24,  1920,  the  record  being  continuous  since 
February  24,  1919,  a  period  of  19  months  and  including  two  entire 
seasons. 


ULY 

II 

I9Z( 

fi- 

M 

1 

5 

n 

a 

0 

1 

•  1 

±1- 

^^— 

•—  -  — 

;==» 

>-  — 

—  t 

•fl— 

•- 

—  r^Z 

- 

- 

__-•—• 

MARCH 

5  1920 

__ 

FIG.  10. — Dendrographic  records  of  California  live  oak  (Quercus  agrifolid)  No.  2.  Beginning 
growth,  denoted  by  upward  course  of  the  tracing,  is  shown  in  the  week  beginning  March  15,  1920, 
and  vigorous  growth  in  week  beginning  May  31.  Quiescence  with  small  daily  variations  are  seen 
in  week  beginning  July  11.  Variations  are  X  15  on  a  scale  of  10  mm.  intervals. 

The  measurements  of  a  second  oak  were  taken  for  1920  by  an  instru- 
ment in  wrhich  the  floating  frame  was  make  up  of  three  bars  of  invar 
and  one  bar  of  bario.  The  bark  was  intact  and  turgid,  the  trunk 
having  a  circumference  of  54  cm.  at  the  place  of  measurement,  1.3 
meters  above  the  ground.  The  levers  were  set  to  amplify  16  times  and 
a  thermometer  was  set  in  the  bark  to  take  temperatures  of  the  north 
side  at  about  a  centimeter  below  the  surface.  No  growth  was  to  be 
seen  in  the  tips  of  the  branches  of  this  tree  on  February  11,  1920, 

1  The  above  statements  are  in  part  corrections  of  the  preliminary  report  on  this  tree :  The  growth 
of  an  oak  trunk.  Carnegie  Inst.  Wash.  Year  Book  for  1919,  see  p.  77. 


GROWTH    IN   TREES. 


33 


although  others  in  more  exposed  localities  had  made  elongations  of 
2  to  4  cm.  of  the  leafy  shoots.  A  temperature  of  8°  C.  was  taken  on 
March  30,  and  not  until  April  1  was  an  upward  movement  of  the  pen 
to  be  seen,  the  record  for  the  previous  6  weeks  being  a  level  line  with 
but  little  daily  variation. 

Steady  and  continuous  enlargement  of  the  trunk  continued  until 
June  20.  After  a  period  of  quiescence,  enlargement  again  began  on 
July  3,  continuing  until  July  25.  A  total  increase  of  4.5  mm.  in 
diameter  had  taken  place  (fig.  10). 

After  a  period  of  quiescence,  with  no  indication  of  further  seasonal 
enlargement,  five  drain  tiles,  75  cm.  long,  were  set  vertically  in  the 
loose  sandy  soil  around  the  tree  within  a  radius  of  2  meters  from  the 
trunk,  and  water  was  turned  into  these  openings  so  that  2,000  gallons 
were  taken  in  without  overflow  between  5h  30m  p.  m.  of  August  1  and 


AUG    30  1920 


AUG.   16    920 


FIG.  11. — Dendrographic  records  of  California  live  oak  No.  2  illustrated  in  fig.  10.  A  condition 
of  quiescence  had  been  reached  when  irrigation  was  begun  before  6  p.  m.  on  August  16,  with  a 
quick  response  in  increase  in  diameter  which  continued  through  the  week  and  until  the  middle 
of  the  following  week,  as  shown  in  the  record  in  the  middle  of  the  figure.  Quiescence  with  but 
little  daily  variation  is  indicated  in  the  record  of  the  week  beginning  August  30.  Some  shrinkage 
ensued  in  the  week  beginning  September  6,  1920.  Variations  are  X  15  on  a  scale  with  10  mm. 
intervals. 

7h  30m  a.  m.  the  next  morning,  and  1,000  gallons  were  added  on  the 
second  night.  The  soil  previous  to  irrigation  had  become  so  dry  that 
it  had  a  moisture  content  of  less  than  6  per  cent.  The  consequences 
of  the  irrigation  were  extremely  startling.  Within  2  hours  an  enlarge- 
ment was  recorded  by  the  dendrograph,  which  continued  so  that  during 
this  week  an  actual  increase  of  about  0.5  mm.  had  taken  place  in  the 
diameter  of  the  trunk,  including  the  bark.  The  rate  soon  slackened, 
however,  and  no  growth  was  visible  on  August  27,  at  which  time  a 
total  accretion  of  1  mm.  had  been  made  to  the  diameter  (fig.  11). 


34 


GROWTH   IN   TREES. 


The  experiment  was  repeated  by  giving  the  soil  around  the  tree 
2,000  gallons  at  9  p.  m.  on  September  15.  Again  a  swelling 
was  noticeable  within  4  hours  after  the  water  was  laid  on,  and  not 
more  than  800  gallons  had  been  given  the  soil.  Enlargement  con- 
tinued for  3  days,  with  a  total  addition  of  0.3  mm.  to  the  thickness  of 
the  trunk.  In  the  ensuing  quiescent  period  no  shrinkage  occurred, 
and  no  swelling  resulted  from  the  rains  of  October  6  and  8.  The 
instrument  was  now  dismounted. 

The  readiness  of  reaction  of  the  live  oak  to  increased  soil-water 
supply  and  the  shorter  period  of  enlargement  and  small  relative  total 
are  in  contrast  with  the  reactions  of  the  pine  growring  in  similar  soil 
a  few  meters  distant.  The  root  system  has  been  described  by  Cannon 
as  including  a  well-developed  superficial  portion  consisting  of  numerous 
short,  slender  roots  which  lie  within  a  meter  of  the  surface.1  The 
method  of  irrigation  was  calculated  to  wet  the  absorbing  surfaces  of 
these  roots  The  actual  path  to  be  traversed  from  the  absorbing  surfaces 

MARCH   KH7 


• 

I.  fip 

IB 

vr, 

M     ! 

ft.    6p.Jll2P-M.6AM. 

H  6PM.12 

-M.6AK   M.  6PIC.12PJf.8AJl   M.  6PH.12P.M6A.M.    M.  6P.M.  12PM  6A.M.    M.  6P.M.  12  P*  6A.M. 

-  —  s^ 

./- 

-  —  ^ 

-**^_ 

—  .. 

2 

"^  1 

^-*-^_ 

•- 

FIQ.  12. — Dendrographic  record  of  growth  and  variations  in  Arizona  ash  (Fraxinut  ortzontco) 
for  the  week  beginning  March  10, 1919.  Temperature  of  cambium  region  ranged  from  6°  to  24°  C 
A  period  of  temperatures  from  6°  to  9°  C.  on  the  15th  and  16th  was  characterized  by  little, 
shrinkage.  Variations  are  X  10  on  a  scale  ofk!0  mm.  intervals. 

to  the  part  of  the  trunk  in  which  swelling  was  measured  was  not  less 
than  2  meters,  and  this  was  traversed  by  the  water  supply  in  such 
quantity  as  to  be  measurable  in  less  than  4  hours. 

GROWTH  OF  THE  ARIZONA  ASH. 

The  Arizona  ash  (Fraxinus  arizonica),  a  rapidly  growing  species 
which  forms  a  trunk  25  to  50  cm.  in  diameter,  occurs  along  streamways 
in  Arizona  and  New  Mexico.  It  is  planted  around  dwellings  and  the 
size  attained  appears  to  bear  a  direct  relation  to  the  available  water 
supply. 

A  dendrograph,  with  a  floating  frame  of  bario  having  two  bearing 
points  opposite  the  lever,  was  attached  to  a  tree  near  the  residence 
of  Dr.  H.  W.  Fenner,  in  Tucson,  Arizona,  on  March  8,  1919,  and  a 
thermometer  was  thrust  under  the  bark.  The  instrument  was  set 
to  amplify  the  variations  ten  tunes  in  the  record.  The  trunk  was 
almost  exactly  1  meter  in  circumference  and  was  compressed  in  one 
diameter.  Irrigation  practice  had  begun  for  the  season  and  the 

Cannon,  W.  A.  Tree  distribution  in  central  California.  Pop.  Sci.  Monthly,  86:417:424. 
Nov.  1914.  See  pp.  420-421  and  fig.  3. 


GROWTH   IN   TREES. 


35 


ground  was  already  saturated  about  the  tree.  The  flower  buds  were 
beginning  to  move,  but  were  not  so  far  advanced  as  some  that  were 
seen  on  unirrigated  land  in  the  vicinity.  The  conditions  were,  in  fact, 
as  if  the  plant  were  growing  along  a  water-course  in  its  natural 
habitat  (fig.  12). 

Enlargement  began  on  March  10  and  continued  at  such  rate  that 
an  enlargement  of  4  mm.  had  taken  place  by  April  7,  a  period  of 
28  days  (fig.  13).  A  period  of  depression  and  shrinkage,  for  5  days 
during  a  cold  storm,  was  followed  by  a  resumption  of  growth  which 
continued  until  August  25.  Another  period  of  depression  ensued, 
but  6  days  afterwards  enlargement  was  again  noticeable  which  lasted 
for  a  week,  and  other  such  impulses  were  displayed  in  September  and 


MAY     5-IZ    IS 

13 

•U.6A.M     M  BPJI  12pu6AJt 

lit  6PM  12 

».M  6.    M       M.  6P-M  12PJL  6A.M 

£_ 

•~\ 

X 

^ 

~\ 

/- 

\ 

'/ 

^ 

/ 

/ 

/=" 

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V 

/ 

? 

—  ^ 

x 

/ 

x 

\ 

/ 

- 

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- 

s 

/ 

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^/ 

I 

Fio.  13. — Dendrographic  record  of  growth  for  the  week  beginning  May  5,  1919,  at  a  time  when 
the  daily  variations  were  at  a  maximum.  Relative  humidity  was  low  and  transpiration  was  high 
during  the  midday  period,  at  which  time  great  shrinkage  look  place.  Variations  X  10  on  a  scale 
of  10  mm. 


OCT.    13-20    1919 

1 

v^_ 

_ 

—  *-x. 

,  

^_ 

X" 

^X_ 

~- 

•>«. 

-— 

, 

FIQ.  14. — Variations  in  Arizona  ash  during  a  final  period  of  slow  enlargement  near  the  close  of 
the  season,  October  13  to  20,  1919.  Variations  X  10  on  a  scale  of  10  mm.  intervals. 

October  (fig.  14) ;  after  this  equalizing  variations  of  diminishing  ampli- 
tude only  were  seen  until  leaf -fall  occurred  about  November  17  to  24, 
after  which  the  record  was  nearly  a  level  line  until  January. 

The  total  increase  in  the  diameter  of  the  tree  during  the  season 
amounted  to  about  26  mm.,  and  a  core  taken  from  the  trunk  below  the 
bearings  on  April  20,  1921,  showed  a  layer  of  12  mm. 

This  instrument  was  replaced  by  a  new  setting  on  January  10,  1920, 
with  an  amplification  of  5  times,  and  the  record  was  a  continued  level 
line  until  April,  when  some  equalizing  daily  variations  began  which 
were  the  only  changes  until  June  10.  An  enlargement  now  began 
which  continued  until  about  July  20  with  a  depression  of  the  rate  in 
the  last  week  in  June,  which  may  be  coupled  with  the  high  temperatures 
and  insufficient  water  supply  of  that  period.  Then  followed  only 


36  GROWTH  IN  TREES. 

equalizing  variations,  which  decreased  in  amplitude  with  the  advance 
of  the  season,  until  the  record  was  but  little  away  from  a  level  line 
until  January  1921,  when  the  instrument  was  dismounted  to  be  re- 
placed by  one  of  improved  pattern.  The  total  increase  during  1920 
amounted  to  12  mm.,  or  about  one-half  that  of  the  previous  year. 
The  reduction  of  the  measurements  given  was  in  fair  agreement  with 
measurements  of  cores  taken  from  the  tree  in  February  1921.  The 
wood  formed  at  the  beginning  of  the  season  is  characterized  by  ex- 
tremely large  vessels,  which  serve  to  denote  the  part  of  the  layer  formed 
earliest  in  the  spring.1 

Vines  has  described  the  annual  rings  of  Fraxinus  excelsior  as  being 
2  to  3  mm.  in  thickness  and  as  consisting  of  an  internal  spring  zone 
of  wide  vessels  with  wood-parenchyma  and  rather  thin-walled  woody 
fibers,  external  to  which,  later  in  the  season,  thick-walled  woody 
fibers  form  with  scattered,  smaller  vessels  surrounded  by  wood  paren- 
chyma. The  wood  formed  at  the  close  of  the  season  consists  chiefly 
of  wood  parenchyma  and  small,  very  thick-walled  vessels.  He  notes 
that  young  trees  of  this  species  in  a  damp  soil  may  form  a  layer  of 
wood  15  mm.  in  thickness  in  a  season,  which  is  practically  equivalent 
to  that  of  the  Arizona  ash  under  conditions  of  irrigation.2 

The  daily  variation  in  1919  was  greater  than  that  seen  at  any  other 
time  or  in  any  other  tree.  Thus  the  daily  shrinkage  in  March  might 
be  as  much  as  0.4  mm.,  with  an  over-compensating  increase  of  0.6  mm. 
by  the  following  morning;  in  April  these  measurements  were  1.1  mm. 
and  1.4  mm.  In  May  the  variations  rose  to  1.6  and  2.1  mm.  Cor- 
related variations  are  displayed  by  elongating  seedlings  of  the  ash 
during  the  same  months. 

The  materials  of  which  the  floating  frames  were  constructed  were 
tested  to  determine  whether  or  not  some  of  this  apparent  variation 
might  be  due  to  shortening  and  lengthening  of  the  metal  bars  and  rods 
under  changing  temperatures. 

Calibrations  of  a  bar  of  bario,  such  as  was  used  in  this  instrument, 
showed  that  its  variation  was  0.0000065  per  unit  part  with  1°  C.  The 
length  of  the  axis  of  the  yoke  was  14.5  inches  or  363  mm.,  and  its 
variation  would  therefore  be  0.000025  mm.  for  1°,  and  0.0005  mm. 
for  20°,  which  would  represent  the  possible  total  in  any  one  day.  This 
amplified  10  times  by  the  levers  would  amount  to  about  1/200  of  one 
space  on  the  record  sheet.  This  would  be  wholly  compensated  by  the 
expansion  and  contraction  of  the  short  contact  screws  and  by  the  varia- 
tion in  the  instrument,  so  that  for  the  purposes  of  this  research  the 
instrumental  error  may  be  neglected. 

1  The  above  calculations  are  to  be  used  in  correction  of  the  statements  in  the  Carnegie  lust. 
Wash.  Year  Book  for  1919,  p.  74. 
*  Vines,  8.  H.     Text  Book  of  Botany,  p.  198.     1895. 


GROWTH  IN  TREES. 


37 


GROWTH  OF  A  BEECH  TREE. 

An  instrument  with  a  floating  frame  of  bario  of  the  U-form  was 
put  in  place  on  a  beech  tree  (Fagus  grandifolia)  on  the  grounds  of 
Johns  Hopkins  University  at  Baltimore  on  April  16,  1919,  about  the 
time  development  of  the  leaves  was  beginning.  In  addition  to  the 
somewhat  irregular  daily  variations  swellings  were  seen  as  a  conse- 
quence of  rains  with  subsequent  shrinkage.  Not  until  May  18,  when 
the  tree  was  in  full  leafage,  did  some  increase  show  in  the  record. 
This  continued  until  May  30,  after  which  equalizing  variations  ensued, 
which  continued  until  mid-July.  A  week  of  rains  was  followed  by 
enlargements  which  continued  for  a  month  and  had  a  net  total  of 
about  half  that  of  the  spring  growth  in  May  and  June. 

Now  followed  a  period  of  regular  equalizing  daily  variations,  which 
terminated  about  September  14.  The  ensuing  enlargement,  which 
lasted  for  3  weeks,  showed  a  total  increase  less  than  hi  the  preceding 
active  period.  Only  equalizing  variations  were  now  seen  and  the  in- 
strument was  dismounted  early  in  October.  The  total  accretion  to 
the  diameter  amounted  to  about  4.5  mm.  (fig.  15). 

EQUALIZING  DAILY  VARIATIONS  IN  DIAMETER. 

The  equalizing  changes  in  the  trunk  are  such  that  the  diameter  is 
least  at  midday  or  in  the  afternoon,  when  the  temperature  of  the  trunk 
is  highest.  The  difference  between  the  readings  of  a  thermometer 
thrust  under  the  bark  in  early  morning  and  at  noontime  is  never  more 
than  8°  C.  or  at  most  10°  C.,  while  that  in  the  center  of  the  trunk  may 
be  no  more  than  a  degree  or  two.  Whatever  the  temperature  might 
be,  a  rise  would  tend  to  expand  the  woody  column.  Dendrographic 
and  other  measurements  show  a  decrease  at  this  tune.  The  trunk  is 
seen  to  shrink  at  a  time  when  the  temperature  is  highest.  It  is  obvious, 
therefore,  that  we  must  look  to  causes  other  than  a  direct  temperature 
effect. 

The  first  possibility  to  be  tested  was  that  of  the  water  relations  of  the 
bark,  and  Monterey  pine  No.  7  was  chosen  for  this  purpose.  A  small 
section  of  bark  and  bast  was  removed  from  the  north  side  of  the  tree 
below  the  instrument,  and  these  two  formations  were  separated  and 
placed  under  the  auxographs  in  the  dark  room  in  which  swelling  liquids 
now  stood  at  12°  C.  The  results  are  as  below: 


Constituents. 

Bast. 

Cork. 

Water 

12.5  p.  ct. 

0  p.  ct. 

HC1  .01  N  

5 

20 

NaOH  .01  N  
Glvcocoll  01  M 

7.5 
10 

15 
10 

209253 


38 


GROWTH  IN  TREES. 


The  bast  layer  measured  about  2  mm.  in  thickness  throughout  and 
seemed  fairly  moist.  The  cork  layer  measured  was  light  in  color,  pre- 
sumably had  been  formed  during  the  current  season,  and  varied  from 
0.8  to  1  mm.  in  thickness.  It  was  easily  separable  from  the  older 
darker  layers  outside  of  it.  The  swelling  of  the  bast  was  complete 
in  2  hours  in  the  acid,  4  hours  in  the  alkali,  and  about  7  or  8  hours  in 
the  glycocoll,  while  increase  in  water  continued  for  nearly  a  day.  The 
swelling  of  the  new  cork  in  the  acid  went  on  at  a  very  slow  rate  for 
about  2  days,  while  it  continued  for  5  days  in  the  alkali.  It  was  com- 
plete in  the  glycocoll  solution  in  about  10  or  12  hours. 


FIG.  16. — Dendrographic  records  of  American  beech  (Fopus  grandifolia) ,  showing  only  slight 
daily  variations  in  April,  increases  beginning  late  in  May  and  continuing  until  September. 

Separate  samples  of  cork  and  bast  were  taken  from  another  place 
on  the  trunk  and  sections  were  tested  with  the  auxograph  to  ascertain 
the  water  deficit  of  these  tissues  after  a  week  in  which  growth  had 
come  to  a  standstill,  presumably  on  account  of  the  dry,  hot  days. 
These  sections  were  swelled  at  12°  C.  and  the  results  are  as  below: 


Solutions. 

Bast. 

Cork. 

Water  
HC1.01  N  

7.5  p.  ct. 
10 

6p.ct. 
g 

NaOH.Ol  N  
Glycocoll  .01  M  

22 
15 

10 
20 

GROWTH   IN   TREES. 


39 


These  swellings  were  concluded  at  the  end  of  3  days,  the  course  of 
enlargement  being  much  as  has  been  previously  described.  The 
record  of  the  variation  in  size  of  the  trunk  during  this  period  showed 
that  the  woody  trunk  made  a  daily  variation  practically  equivalent  to 
that  of  the  entire  tree. 

These  results  show  that  the  cork  in  one  instance  was  impervious  to 
water  and  remarkably  so  to  the  other  solutions.  The  bast,  of  course, 
takes  up  water  readily  and  is  easily  penetrated  by  other  solutions, 
especially  the  hydroxid  and  amino-acid.  These  results  may  be  taken 
to  indicate  the  possibility  of  some  transpiration  through  the  bark, 
although  this  matter  was  not  tested,  directly.  On  May  22  a  dendro- 
graph  was  attached  to  a  tree  about  35  cm.  in  diameter,  standing  on 
the  north-facing  slope  north  of  the  laboratory,  for  the  purpose  of 


FIG.  16. — Dendrographic  record  of  Monterey  pine  No.  7,  to  show  relative  amount  of  variation 
In  outer  and  inner  parts  of  trunk.  The  record  for  the  week  beginning  May  24  ie  for  the  entire 
trunk,  the  bearings  being  taken  from  an  inner  thin  layer  of  cork.  All  other  records  are  from 
bearings  taken  from  the  woody  cylinder  internal  to  that  of  1918.  The  range  of  the  daily  variation 
of  the  inner  cylinder  is  seen  to  be  less  in  the  earlier  part  of  the  season  and  to  decrease  with  the 
season,  as  shown  in  the  record  for  the  week  beginning  August  30.  A  slight  increase  was  seen  in  the 
week  beginning  October  4.  Variations  are  X  25  on  a  scale  of  10  mm.  intervals. 

measuring  the  relative  expansion  of  the  cork  and  cambium  layers  and 
of  the  wood.  The  plan  was  to  attach  the  instrument  to  the  tree  entire 
and  to  obtain  the  record  of  the  daily  course  of  change,  and  then  strip 
off  the  bark  and  growing  layer  and  place  the  contacts  of  the  instrument 
on  the  trunk  itself.  The  trunk  was  seen  to  be  undergoing  daily 
equalizing  variations  with  no  growth  in  progress.  Pine  No.  6,  a  few 
meters  distant,  was  still  showing  some  accretion,  but  with  a  steadily 
lessening  rate. 


40  GROWTH   IN   TREES. 

After  the  corky  bark  and  the  softer  bast  had  been  removed,  leaving 
the  woody  surface  bare  for  about  5  sq.  cm.  in  two  places,  to  give  bearings 
for  the  contact  screw  and  lever  arm,  the  daily  equalizing  variation  in 
diameter  for  a  week  had  an  amplitude  of  0.2  mm.  or  one  part  in  1,750 
equivalent  to  a  change  of  400  cu.  cm.  in  volume.  At  the  end  of  this 
time  the  layers  of  wood  formed  in  1920  and  1918  were  removed,  giving 
a  new  reduced  diameter  of  30  cm.  After  the  bearings  were  adjusted 
on  these  sunken  surfaces,  the  daily  variation  (which  at  first  was  prac- 
tically equivalent  to  that  of  the  preceding  setting  of  the  whole  trunk) 
decreased  until  August,  when  the  range  of  variation  was  about  1  in 
8,750  parts,  a  range  which  was  maintained  with  interruptions  until 
the  close  of  the  observations  in  October.  The  variation  in  the  volume 
of  the  wood  amounted  to  about  80  cu.  cm.  (fig.  16). 

In  comparison  with  the  above,  it  was  noted  that  the  relative  range 
of  the  daily  equalizing  variations  in  Pine  No.  6  decreased  in  the  same 
ratio,  both  reaching  an  approximate  minimum  about  September  20. 
The  behavior  of  the  two  diverged  after  this  date.  The  dendrographic 
record  of  the  entire  trunk  of  No.  6  shows  an  increase  in  the  range  of 
daily  variation,  to  which  was  added  a  positive  increase  accompanying 
a  rain  on  October  6,  which  continued  until  the  12th,  when  only  the 
equalizing  variations  continued,  but  these  were  of  an  amplitude  about 
twice  that  of  the  minimum.  The  woody  cylinder  of  No.  7  ulterior  to 
the  layer  of  1919  also  showed  a  swelling  of  the  same  duration  as  in 
Nov  6,  but  the  range  of  daily  variation  did  not  increase. 

Thermometers  were  inserted  in  the  trunk  of  No.  7  on  June  1,  one 
to  take  the  temperature  of  the  bast  and  cambium  region  and  a  second 
with  its  bulb  at  a  distance  of  12  cm.  from  the  surface,  which  would 
be  within  less  than  8  cm.  of  the  center.  The  course  of  the  tempera- 
tures during  the  day  and  with  the  advance  of  the  seasons  may  be 
illustrated  by  the  following  data:  At  8  a.  m.  the  outer  thermometer 
read  12°  C.  and  the  inner  13°  C.,  at  6  p.  m.  the  readings  were  identical. 
On  July  2  the  outer  temperature  at  7  a.  m.  was  14°  C.,  and  the  inner 
15°  C.;  at  3  p.  m.  the  readings  were  17°  C.  and  15.5°  C.,  and  at  6  p.  m. 
identical  readings  of  16°  C.  were  taken.  On  August  8  the  outer 
temperature  was  12°  C.  at  7h  30m  a.  m.,  and  the  inner  13°  C.  At 
lh  30m  p.  m.  the  outer  temperature  had  advanced  to  15°  C.  and  the 
inner  to  13.5°  C.  The  range  of  temperature  in  the  tree  taken  by  the 
two  thermometers  was  8°  C.  during  the  summer,  and  the  difference 
between  the  outer  and  inner  readings  reached  its  maximum  of  5°  C. 
in  mid-afternoon,  or  earlier  on  still  hot  days,  equalization  of  the  two 
being  reached  shortly  after  sunset,  with  the  outer  portion  of  the  tree 
becoming  cooler  during  the  night,  so  that  at  sunrise  as  much  of  a  dif- 
ference as  1.5°  C.  might  be  seen. 

The  diameter,  therefore,  had  its  minimum  measurement  at  the  time 
when  the  outer  layers  of  the  trunk  have  a  maximum  temperature. 


GROWTH   IN   TREES.  41 

Such  high  temperature,  with  its  attendant  conditions  of  low  relative 
humidity  and  the  local  maximum  of  air-flow,  would  of  course  heighten 
the  rate  of  water  loss  of  the  entire  tree.  Such  water  loss  would,  of 
course,  take  place  from  the  entire  surface,  and  although  it  may  be 
assumed  that  the  rate  per  unit  area  from  the  trunk  would  be  small, 
it  is  yet  undetermined. 

Water  is  entering  the  tree  through  the  outer  membranes  of  the  roots 
at  all  times,  in  accordance  with  the  balance  between  the  soil  mois- 
ture content  of  the  soil  and  the  absorbing  capacity  of  the  roots.  It 
passes  upward  by  capillarity  through  the  vessels  at  a  rapid  rate  and 
through  the  system  of  inclosed  wood-cells  or  tracheids  at  a  slower  rate. 
The  mass  of  these  woody  cells  furnishes  a  structure,  however,  upon 
which  may  be  based  an  explanation  of  the  shrinkage  of  the  trunk. 

Such  an  explanation  must  take  into  account  the  fact  that  the  rate 
of  absorption  by  the  roots  shows  but  little  daily  variation,  due  espec- 
ially to  the  fact  that  the  temperature  of  the  soil  may  vary  but  little 
at  the  depth  at  which  the  roots  lie.  The  rate  of  transpiration,  how- 
ever, which  may  come  down  to  a  low  minimum  during  the  night  fogs 
characteristic  of  the  region,  may  rise  to  a  high  maximum  during  a 
warm  sunny  day  with  a  marked  air-flow.  The  water  thus  lost  is 
withdrawn  from  the  wood,  either  by  direct  outward  exit  through  the 
bark  or  upward  through  the  branches  and  out  through  the  leaves. 
In  both  cases  the  withdrawal  lessens  the  supply  or  balance  in  the  sys- 
tem of  tracheids. 

The  wood  of  the  1919  layer,  when  freshly  taken  from  the  tree  in 
slips  less  than  2  mm.  in  thickness,  swelled  1  per  cent  in  water  and  in 
NaOH  0.01N,  while  the  increase  was  greater  in  HC1  0.01N,  being 
3  per  cent  of  the  original  thickness.  It  is  thus  to  be  seen  that  the 
woody  tracts  through  which  water  passes  upward  in  the  tree  may  have 
a  water  deficit  of  1  part  in  100  when  swelled  in  water  at  a  time  when 
the  actual  daily  shrinkage  amounted  to  but  1  in  1,700  of  the  entire 
diameter.  It  is  highly  probable,  however,  that  the  deficit  is  unequally 
distributed,  being  greater  in  the  outermost  layers. 

These  and  other  important  physical  problems  are  dealt  with  in 
dendrographic  measurements  being  carried  on  at  the  Desert  Labora- 
tory, at  the  Coastal  Laboratory,  and  at  other  places  by  collaborators. 


8T  43 


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